Heat exchanger for fuel cell systems and electrolyser systems and systems comprising the same

Abstract

A heat exchanger for use within a fuel cell or electrolyser system. The device comprises four distinct flow paths arranged to facilitate thermal transfer between incoming reactants and heat sources. The heat exchanger includes two heated paths, a first path configured to direct a first fluid to an inlet of the fuel cell or electrolyser stack, and a second path configured to direct air from a supply source to a second inlet of the stack. The device includes two heating paths, a first heating path that receives fluid from a dedicated heating source, and a second heating path that receives fluid directly from an outlet of the fuel cell or electrolyser stack. The system is configured such that the first fluid and the intake air are heated via thermal exchange with the fluid from the heating source, the fluid exiting the stack, or a combination of both.

Description

HEAT EXCHANGER FOR FUEL CELL SYSTEMS AND ELECTROLYSER SYSTEMS AND SYSTEMS COMPRISING THE SAME CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is related to Australian Provisional Patent Application No 2025900471, filed on 19 February 2025, the contents of which are incorporated herein by reference in their entirety.FIELD OF THE INVENTION

[0002] The present disclosure relates to a heat exchanger for fuel cell systems and electrolyser systems and fuel cell systems and an electrolyser systems comprising the same. In particular, the present disclosure relates to a heat exchanger for fuel cell systems and electrolyser systems having multiple heating streams.BACKGROUND OF THE INVENTION

[0003] Fuel cell systems typically comprise a fuel cell stack and the balance of plant (BOP). Similarly, electrolyser systems typically comprise an electrolyser stack and the BOP. The BOP of a fuel cell system refers to the components of the fuel cell system apart from the fuel cell stack. Similarly, the BOP of an electrolyser system refers to the components of the electrolyser system apart from the electrolyser stack. The BOP of a fuel cell system and an electrolyser system may include pumps, valves, heat exchangers, sensors, filters, burner and other components required for the fuel cell stack to operate. It will be appreciated that the performance and / or operational characteristics of a fuel cell system and an electrolyser system can be varied / optimised by varying different operational parameters of one or more components of the BOP.

[0004] Fuel cell systems using solid oxide fuel cells (SOFC) are known to produce multiple sources of heat, which can be used as heating sources in heat exchangers to heat other fluids. Similarly, electrolyser systems using solid oxide electrolysers produce multiple sources of heat. Embodiments of the present disclosure provide alternativemethods and systems for using the sources of heat generated by fuel cell systems and electrolyser systems to heat other fluids.SUMMARY OF THE INVENTION

[0005] According to a first aspect of the invention, there is provided a heat exchanger for a fuel cell or electrolyser system, the heat exchanger comprising: a first heated fluid flow path configured to direct a first fluid through the heat exchanger, an outlet of the first heated fluid flow path configured to be coupled in fluid communication with a first inlet of a fuel cell or electrolyser stack of the fuel cell or electrolyser system; a second heated fluid flow path configured to direct air through the heat exchanger, an inlet of the second heated fluid flow path configured to be in fluid communication with a source of air, and an outlet of the second heated fluid flow path configured to be coupled in fluid communication with a second inlet of the fuel cell or electrolyser stack; a first heating fluid flow path configured to direct a first heating fluid from a heating source of the fuel cell or electrolyser system through the heat exchanger, an inlet of the first heating fluid flow path configured to receive the first heating fluid from the heating source; a second heating fluid flow path configured to direct a second heating fluid from the fuel cell or electrolyser stack through the heat exchanger, an inlet of the second heating fluid flow path configured to be coupled in fluid communication with a first outlet of the fuel cell or electrolyser stack, wherein: the first fluid flowing through the first heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path; and air flowing through the second heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path.

[0006] According to a second aspect of the invention, there is provided a fuel cell or electrolyser system comprising: a fuel cell or electrolyser stack; a heating source; a heat exchanger having: a first heated fluid flow path to direct a first fluid through the heat exchanger, an outlet of the first heated fluid fuel flow path coupled in fluid communication with a first inlet of the fuel cell or electrolyser stack; a second heated fluid flow path to direct air through the heat exchanger, an inlet of the second heated fluid flow path is influid communication with a source of air, and an outlet of the second heated fluid flow path coupled in fluid communication with a second inlet of the fuel cell or electrolyser stack; a first heating fluid flow path to direct a first heating fluid from the heating source through the heat exchanger, an inlet of the first heating fluid flow path configured to receive the first heating fluid from the heating source; and a second heating fluid flow path to direct a second heating fluid from the fuel cell or electrolyser stack through the heat exchanger, an inlet of the second heating fluid flow path coupled in fluid communication with a first outlet of the fuel cell or electrolyser stack, wherein: the first fluid flowing through the first heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path; and air flowing through the second heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path.

[0007] There is also disclosed a heat exchanger for a fuel cell system having a fuel cell stack, the heat exchanger comprising: a fuel cell fuel flow path configured to direct fuel through the heat exchanger, an inlet of the fuel cell fuel flow path configured to be coupled in fluid communication with a source of fuel, and an outlet of the fuel cell fuel flow path configured to be coupled in fluid communication with a fuel inlet of the fuel cell stack; an air flow path configured to direct air through the heat exchanger, an inlet of the air flow path configured to be in fluid communication with a source of air, and an outlet of the air flow path configured to be coupled in fluid communication with an air inlet of the fuel cell stack; an exhaust gas flow path configured to direct exhaust gas from a burner of the fuel cell system through the heat exchanger, an inlet of the exhaust gas flow path configured to be coupled in fluid communication with an exhaust outlet of the burner; and an anode-off-gas flow path configured to direct anode-off-gas from the fuel cell stack through the heat exchanger, an inlet of anode-off-gas flow path configured to be coupled in fluid communication with an anode-off-gas outlet of the fuel cell stack, wherein: fuel flowing through the fuel cell flow path is configured to be heated by exhaust gas flowing through the exhaust gas flow path and / or anode-off-gas flowing through the anode-off-gas flow path; and air flowing through the air flow path is configured to be heated by exhaust gasflowing through the exhaust gas flow path and / or anode-off-gas flowing through the anode-off-gas flow path.

[0008] There is also disclosed a fuel cell system comprising: a fuel cell stack configured to generate electricity; a burner configured to generate heat for the fuel cell stack; and a heat exchanger having: a fuel cell fuel flow path to direct fuel through the heat exchanger, an inlet of the fuel cell fuel flow path coupled in fluid communication with a source of fuel, and an outlet of the fuel cell fuel flow path coupled in fluid communication with a fuel inlet of the fuel cell stack; an air flow path to direct air through the heat exchanger, an inlet of the air flow path is in fluid communication with a source of air, and an outlet of the air flow path coupled in fluid communication with an air inlet of the fuel cell stack; an exhaust gas flow path to direct exhaust gas from the burner through the heat exchanger, an inlet of the exhaust gas flow path coupled in fluid communication with an exhaust outlet of the burner; and an anode-off-gas flow path to direct anode-off-gas from the fuel cell stack through the heat exchanger, an inlet of the anode-off-gas flow path coupled in fluid communication with an anode-off-gas outlet of the fuel cell stack, wherein: fuel flowing through the fuel cell flow path is configured to be heated by exhaust gas flowing through the exhaust gas flow path and / or by anode-off-gas flowing through the anode-off-gas flow path; and air flowing through the air flow path is configured to be heated by exhaust gas flowing through the exhaust gas flow path and / or anode-off-gas flowing through the anode-off-gas flow path.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Preferred embodiments of the invention will be described, by way of example only, with reference to the accompanying representations.

[0010] Figure l is a schematic diagram of a natural gas fuel cell system according to an embodiment of the present disclosure;

[0011] Figure 2 is an exemplary schematic layout of the heat exchanger of the fuel cell system of Figure 1;

[0012] Figure 3 is a schematic diagram of a hydrogen fuel cell system according to another embodiment of the present disclosure;

[0013] Figure 4 is a schematic diagram of an electrolyser system according to another embodiment of the present disclosure;

[0014] Figure 5 is a schematic diagram of a reversible fuel cell / electrolyser system according to another embodiment of the present disclosure; and

[0015] Figure 6 is a schematic diagram of a reversible fuel cell / electrolyser system according to another embodiment of the present disclosure..DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] As illustrated in Figure 1, a natural gas fuel cell system 100 includes a heat exchanger 110, a fuel cell stack 130, a burner 140, a pre-reformer 150, an anode-off-gas heat exchanger 160 and a waste-heat-recovery (WHR) heat exchanger 170.

[0017] The heat exchanger 110 defines a fuel cell fuel flow path 111, an air flow path 112, an exhaust gas flow path 113, a burner fuel flow path 114, an anode-off-gas flow path 115 and a water / steam flow path 116. The fuel cell fuel flow path 111 includes a fuel inlet 117 and a fuel outlet 118. The air flow path 112 includes an air inlet 119 and an air outlet 120. The exhaust gas flow path 113 includes an exhaust gas inlet 121 and an exhaust gas outlet 122. The burner fuel flow path 114 includes a burner fuel inlet 123 and a burner fuel outlet 124. The anode-off-gas flow path 115 includes an anode-off-gas inlet 125 and an anode-off-gas outlet 126. The water / steam flow path 116 includes a water inlet 127 and a steam outlet 128.

[0018] As Figure 1 illustrates, the flow direction of the exhaust gas flow path 113 and the anode-off-gas flow path 115 through the heat exchanger 110 is opposite to that of the fuel cell fuel flow path 111, air flow path 112, burner fuel flow path 114 and water / steam flow path 116. The gas streams following exhaust gas flow path 113 and anode-off-gas flow path 115 are heating streams configured to provide heat to the gas streams following fuel cell fuel flow path 111, air flow path 112, burner fuel flow path 114 and water / steam flow path 116.

[0019] The fuel cell stack 130 comprises one or more fuel cells, such as solid oxide fuel cells. The fuel cell stack 130 includes a fuel inlet 131, an anode-off-gas outlet 132, an airinlet 133 and an air outlet 134. Fuel inlet 131 is arranged to provide fuel to the anode of the fuel cells of the fuel cell stack 130, while air inlet 133 is arranged to provide air to the cathode of the fuel cells of the fuel cell stack 130.

[0020] The burner 140 is configured to combust fuel to generate heat, which is used to heat fuel and air in the heat exchanger 110 to a required temperature (discussed below) before flowing into the fuel cell stack 130. The required temperature of the air and fuel flowing into the fuel cell stack 130 may be dependent on the type of fuel cell(s) used in the fuel cell stack 130. The burner 140 includes an air inlet 141, a fuel inlet 142, a cooling air inlet 143 and an exhaust outlet 144. The burner 140 also includes a spark rod 145 for igniting fuel to start the burner 140. The heat generated by the burner 140 may also be used to heat other streams flowing though the heat exchanger 310 (discussed below).

[0021] The pre-reformer 150 includes an inlet 151 and an outlet 152. A steam venturi 153 associated with the pre-reformer 150 is in fluid communication with a source of natural gas 154. Although the outlet 152 is split into two, it is envisaged that there may only be a singular outlet 152. Splitting the outlet 152 into two may improve the flow conditions out of the pre-reformer 150.

[0022] The anode-off-gas heat exchanger 160 includes an anode-off-gas inlet 161, a burner fuel outlet 162 and a burner fuel flow path 163 extending through the anode-off-gas heat exchanger 160 between the anode-off-gas inlet 161 and the burner fuel outlet 162. The anode-off-gas heat exchanger 160 also includes a cooling water inlet 164, a cooling water outlet 165 and a cooling water flow path 166 extending through the anode-off-gas heat exchanger 160 between the cooling water inlet 164 and the cooling water outlet 165. The cooling water inlet 164 is coupled in fluid communication with a source of cooling water 167, which may be mains water or any suitable source of water. Water flowing out of the cooling water outlet 165 may be appropriately discharged or may be cooled by any suitable cooling systems before being returned to the cooling water inlet 164. Alternatively, or additionally, heated water flowing out of the cooling water outlet 165 may be used for other suitable heating purposes (e.g. hot water for showering, swimming pool heating, hydronic heating systems, small industrial heating purposes).

[0023] The WHR heat exchanger 170 includes an WHR gas inlet 171, an WHR gas outlet 172 and an WHR exhaust gas flow path 173 extending through the WHR heat exchanger 170 between the WHR gas inlet 171 and the WHR gas outlet 172. The WHR heat exchanger 170 also includes a water inlet 174, a water outlet 175 and a water flow path 176 extending through the WHR exchanger 170 between the water inlet 174 and the water outlet 175. The water inlet 174 is coupled in fluid communication with a suitable source of water 177 (such as mains water). Water flowing out of the water outlet 175 may be used for any suitable heating purposes (e.g. hot water for showering, swimming pool heating, hydronic heating systems, small industrial heating purposes), after which it may be returned to the water inlet 174 (e.g. via a storage tank) or appropriately discarded.

[0024] The fuel inlet 117 of the heat exchanger 110 is coupled in fluid communication with the outlet 152 of the pre-reformer 150 by a fuel conduit 178. The fuel outlet 118 of the heat exchanger 110 is coupled in fluid communication with the fuel inlet 131 of the fuel cell stack 130 by a fuel conduit 179. The anode-off-gas outlet 132 of the fuel cell stack 130 is coupled in fluid communication with the anode-off-gas inlet 125 of the heat exchanger 110 by a anode-off-gas conduit 180. The anode-off-gas outlet 126 of the heat exchanger 110 is coupled in fluid communication with the anode-off-gas inlet 161 of the anode-off-gas heat exchanger 160 by an anode-off-gas conduit 181. The burner fuel outlet 162 of the anode-off-gas heat exchanger 160 is coupled in fluid communication with the burner fuel inlet 123 of the heat exchanger 110 by a burner fuel conduit 182. The burner fuel outlet 124 of the heat exchanger 110 is coupled in fluid communication with the fuel inlet 142 of the burner 140 by a burner fuel conduit 183.

[0025] The burner fuel conduit 182 is coupled in fluid communication with the steam venturi 153 by a recirculation conduit 184. The recirculation conduit 184 allows fuel flowing in the burner fuel conduit 182 to flow to the steam venturi 153. The flow rate of fuel flowing into the recirculation conduit 184 from the burner fuel conduit 182 may be controlled by any suitable means (e.g. a valve) associated with the recirculation conduit 184.

[0026] A burner fuel bypass conduit 197 connects the burner fuel conduit 182 in fluid communication with the burner fuel conduit 183 bypassing the heat exchanger 110. Theburner fuel bypass conduit 197 may be selectively opened to allow burner fuel flowing in the burner fuel conduit 182 to bypass the burner fuel flow path 114 of the heat exchanger 110 by allowing burner fuel to flow into and through the burner fuel bypass conduit 197 to the burner fuel conduit 183. The burner fuel bypass conduit 197 may be selectively opened and closed by any suitable means (e.g. a valve).

[0027] The air inlet 119 of the heat exchanger 110 is in fluid communication with a source of air 185 via a process air conduit 186. The air outlet 120 of the heat exchanger 110 is coupled in fluid communication with the air inlet 133 of the fuel cell stack 130 by an air conduit 187. The air outlet 134 of the fuel cell stack 130 is coupled in fluid communication with the air inlet 141 of the burner 140 by a burner air inlet conduit 188. The cooling air inlet 143 of the burner 140 is in fluid communication with the source of air 185 by a cooling air conduit 189. A cooling air bypass conduit 190 connects the process air conduit 186 in fluid communication with the air conduit 187 bypassing the heat exchanger 110. The cooling air bypass conduit 190 may be selectively opened to allow air flowing in the process air conduit 186 to bypass the air flow path 112 of the heat exchanger 110 by allowing air to flow into and through the cooling air bypass conduit 190 to the air conduit 187. The cooling air bypass conduit 190 may be selectively opened and closed by any suitable means (e.g. a valve).

[0028] The exhaust outlet 144 of the burner 140 is coupled in fluid communication with the exhaust gas inlet 121 of the heat exchanger 110 by an exhaust gas conduit 191. The exhaust gas outlet 122 of the heat exchanger 110 is coupled in fluid communication with the WHR gas inlet 171 of the WHR heat exchanger 170 by a exhaust gas conduit 192. An exhaust gas bypass conduit 193 connects the exhaust gas conduit 191 in fluid communication with the exhaust gas conduit 192. The exhaust gas bypass conduit 193 may be selectively opened to allow exhaust gas flowing in the exhaust gas conduit 191 to bypass the exhaust gas flow path 113 of the heat exchanger 110 and flow directly to the WHR heat exchanger 170 via the exhaust gas bypass conduit 193 and the exhaust gas conduit 192. The exhaust gas bypass conduit 193 may be selectively opened and closed by any suitable means (e.g. a valve) associated with the exhaust gas bypass conduit 193.

[0029] The water inlet 127 of the heat exchanger 110 is in fluid communication with a source of water 194 (e.g. mains water, deionised water, or any other suitable source of water). The steam outlet 128 of the heat exchanger 110 is connected in fluid communication with the inlet 151 of the pre-reformer 150 by a steam conduit 195. The steam venturi 153 is in fluid communication with the steam conduit 195. The steam venturi 153 is configured such that steam flowing in the steam conduit 195 to the inlet 151 of the pre-reformer 150 draws natural gas from the source of natural gas 154 into the steam conduit 195 through the steam venturi 153. The steam venturi 153 is also configured such that steam flowing in the steam conduit 195 to the inlet 151 of the pre-reformer 150 draws fuel from the recirculation conduit 184 into the steam conduit 195 through the steam venturi 153.

[0030] Operation of the natural gas fuel cell system 100 will be described below.

[0031] Water flows from the source of water 194 into the water / steam flow path 116 of the heat exchanger 110 through the water inlet 127. As the water flows through the water / steam flow path 116, the water is converted to steam by heat provided by anode-off-gas flowing in the anode-off-gas flow path 115 (discussed below) and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 113 (discussed below). The steam exits the water / steam flow path 116 through the steam outlet 128 and flows into and through the steam conduit 195. Steam flows through the steam conduit 195 to the inlet 151 of the pre-reformer 150. During operating conditions, the steam exiting the steam outlet 128 may have a temperature of 700°C, for example.

[0032] Steam flowing through the steam conduit 195 past the steam venturi 153 causes natural gas from the source of natural gas 154 to be drawn into the steam conduit 195 through the steam venturi 153. Similarly, steam flowing through the steam conduit 195 past the steam venturi 153 causes fuel in the recirculation conduit 184 to be drawn into the steam conduit 195 through the steam venturi 153. The steam, natural gas from the source of natural gas 154 drawn into the steam conduit 195 through the steam venturi 153 and any fuel from the recirculation conduit 184 drawn into the steam conduit 195 through the steam venturi 153 form a steam / fuel mixture. The steam / fuel mixture flows into the pre-reformer 150 through the inlet 151.

[0033] The pre-reformer 150 serves to partially reform natural gas in the steam / fuel mixture to reduce the amount of higher hydrocarbons (e.g. ethane, propane, butane) in the steam / fuel mixture. Higher hydrocarbons may cause coking when heated, for example in the fuel cell fuel flow path 111 of the heat exchanger 110. Accordingly, reducing the amount of higher hydrocarbons in the steam / fuel mixture may reduce the amount of coking that may occur in the heat exchanger 110.

[0034] The pre-reformer 150 may use a steam reforming reaction utilising a nickel-based catalyst (or any other suitable pre-reforming catalyst) to convert higher hydrocarbons in the steam / fuel mixture to methane, hydrogen, and carbon oxides to produce a pre-reformed steam / fuel mixture. The steam reforming reaction is an endothermic reaction and the steam in the steam / fuel mixture provides the heat for sustaining this reaction. The pre-reformed steam / fuel mixture exits the pre-reformer 150 through the outlet 152 and flows into the fuel conduit 178. The pre-reformed steam / fuel mixture exiting the outlet 152 of the pre-reformer 150 may have a temperature in the range 350°C-400°C, for example.

[0035] The pre-reformed steam / fuel mixture flows through the fuel conduit 178 and into the fuel cell fuel flow path 111 of the heat exchanger 110 through the fuel inlet 117. The pre-reformed steam / fuel mixture is heated as it flows through the fuel cell fuel flow path 111 by heat provided by anode-off-gas flowing in the anode-off-gas flow path 115 (discussed below) and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 113 (discussed below). The heated pre-reformed steam / fuel mixture exits the fuel cell fuel flow path 111 through the fuel outlet 118 and flows into the fuel conduit 179. The heated pre-reformed steam / fuel mixture exiting the fuel outlet 118 may have a temperature in the range 650°C-750°C, for example. However, depending on the type of fuel cells used in the fuel cell stack 130, the temperature range of the heated pre-reformed steam / fuel mixture exiting the fuel outlet 118 may be between 500°C-900°C. The temperature of the heated pre-reformed steam / fuel mixture exiting the fuel outlet 118 may therefore be controlled to be at a temperature suitable for use with the particular fuel cells being used in the fuel cell stack 130.

[0036] The heated pre-reformed steam / fuel mixture flows through the fuel conduit 179 and into the fuel cell stack 130 through the fuel inlet 131. After entering the fuel cell stack 130 through the fuel inlet 131, the heated pre-reformed steam / fuel mixture is reformed at the anode of the fuel cells of the fuel cell stack 130 to convert methane in the heated prereformed steam / fuel mixture to hydrogen, carbon monoxide and carbon dioxide. This reforming of natural gas at the anode of the fuel cells of the fuel cell stack 130 is referred to as “internal reforming”. For example, the anode of solid oxide fuel cells may comprise nickel, which allows for internal reforming of natural gas in the fuel cell. Although internal reforming has been described above, it is also envisaged that the heated pre-reformed steam / fuel mixture exiting the fuel outlet 118 may be reformed externally to the fuel cell stack 130 in a reformer (not shown) coupled in fluid communication between the fuel outlet 118 of the heat exchanger 110 and the fuel inlet 131 of the fuel cell stack 130.

[0037] The internal reforming of natural gas in the fuel cell stack 130 relies on a steam -methane reforming reaction. The steam-methane reforming reaction reacts methane and steam in the heated pre-reformed steam / fuel mixture in the presence of a catalyst (e.g. nickel based catalysts) to produce hydrogen and carbon monoxide. The steam-methane reforming reaction also utilises a water gas shift reaction to react carbon monoxide and steam in the heated pre-reformed steam / fuel mixture to produce carbon dioxide and hydrogen.

[0038] The fuel cell(s) of the fuel cell stack 130 have suitable anodes, cathodes, and electrolytes / membranes to react hydrogen and oxygen together to generate electricity. Hydrogen produced by the steam-methane reforming reaction (described above) is provided to the anodes of the fuel cell(s) and oxygen in air supplied from the air conduit 187 is provided to the cathodes of the fuel cell(s). The anode of the fuel cell(s) of the fuel cell stack 130 comprises a catalyst (e.g. a nickel based catalyst) that oxidises the hydrogen produced by the steam-methane reforming reaction to produce positively charged hydrogen ions and electrons. The positively charged hydrogen ions react with oxygen ions and the electrons flow through an electrical circuit 135, so producing an electrical current and thus the electrical power output of the fuel cell(s).

[0039] After the oxidation reaction at the anode, the remaining gases exit the fuel cell stack 130 through the anode-off-gas outlet 132. The gases leaving the fuel cell stack 130 through the anode-off-gas outlet 132 are referred to as “anode-off-gas”. Fuel utilisation of the fuel cell stack 130 is the proportion of fuel consumed (i.e. oxidised) by the fuel cell stack 130 compared to the total amount of fuel flowing through the fuel cell stack 130. High fuel utilisations (e.g. greater than 85-90%) may adversely affect the operational life of the fuel cell stack 130. Accordingly, it is preferable to maintain the fuel utilisation of the fuel cell stack 130 within a range of 75-85%. The fuel utilisation of the fuel cell stack 130 may be regulated by adjusting the fuel flow rate supplied to the anode of the fuel cell(s) of the fuel cell stack 130 in response to the measured electrical load, thereby maintaining a desired ratio between fuel flow and electrical current output. However, it will be appreciated that the fuel utilisation of the fuel cell stack 130 may be regulated using any suitable means known in the art.

[0040] Accordingly, a portion of the fuel entering the fuel cell stack 130 will pass through unreacted. Therefore, not all the hydrogen produced by the steam-methane reforming reaction is oxidised at the anode of the fuel cell(s) of the fuel cell stack 130. As a result, the anode-off-gas comprises hydrogen, carbon monoxide, carbon dioxide, and water (in the form of steam). The hydrogen contained in the anode-off-gas flowing out of the fuel cell stack 130 may be redirected to the fuel cell stack 130 using the recirculation conduit 184 and / or supplied to the burner 140 using the burner fuel conduit 182 (discussed below).

[0041] Further, the oxidation reaction at the anode of the fuel cell(s) is exothermic, providing heating of the anode-off-gas. For example, the anode-off-gas may exit the fuel cell stack 130 through the anode-off-gas outlet 132 at a temperature of 650°C - 800°C. However, depending on the type of fuel cells used in the fuel cell stack 130, the temperature of the anode-off-gas exiting the anode-off-gas outlet 132 may vary.

[0042] The anode-off-gas exiting the fuel cell stack 130 through the anode-off-gas outlet 132 flows into and through the anode-off-gas conduit 180. The anode-off-gas flowing through the anode-off-gas conduit 180 flows into the anode-off-gas flow path 115 of the heat exchanger 110 through the anode-off-gas inlet 125. As the anode-off-gas flowsthrough the anode-off-gas flow path 115, the heat from the anode-off-gas is used to heat one or more of the pre-reformed steam / fuel mixture flowing in the fuel cell fuel flow path 111, air flowing in the air flow path 112 (discussed below), burner fuel flowing in the burner fuel flow path 114 (discussed below) and water / steam flowing in the water / steam flow path 116.

[0043] The anode-off-gas is cooled as it flows through the heat exchanger (via the anode-off-gas flow path 115). The cooled anode-off-gas exits the anode-off-gas flow path 115 through the anode-off-gas outlet 126 and flows into the anode-off-gas conduit 181. The cooled anode-off-gas flowing in the anode-off-gas conduit 181 flows into the burner fuel flow path 163 of the anode-off-gas heat exchanger 160 through the anode-off-gas inlet 161 of the anode-off-gas heat exchanger 160.

[0044] Cooling water flowing through the cooling water flow path 166 of the anode-off-gas heat exchanger 160 further cools the anode-off-gas flowing in the burner fuel flow path 163, which condenses at least a portion of any water vapour in the anode-off-gas. The condensed water vapour may then be drained away and recovered, thus reducing the moisture content of the gases flowing out of the burner fuel flow path 163. The condensed water vapour may be drained away via a condensed water outlet (not shown) in the anode-off-gas heat-exchanger 160. The recovered water may be subsequently used for other purposes. For example, the recovered water may be treated (e.g. deionised) and then fed into the water inlet 127 of the heat exchanger 110. The gases flowing out of the burner fuel flow path 163 will be referred to below as “burner fuel”. The burner fuel flows out of the burner fuel flow path 163 through the fuel outlet 162 and into the burner fuel conduit 182.

[0045] Burner fuel flowing in the burner fuel conduit 182 flows into the burner fuel flow path 114 of the heat exchanger 110 through the burner fuel inlet 123. Burner fuel is heated as it flows through the burner fuel flow path 114 by heat provided by anode-off-gas flowing in the anode-off-gas flow path 115 and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 113 (discussed below). The heated burner fuel exits the burner fuel flow path 114 through the burner fuel outlet 124 and flows into the burner fuel conduit

[0046] The heated burner fuel flowing in the burner fuel conduit 183 flows into the burner 140 through the fuel inlet 142. The heated burner fuel flowing into the burner 140 through the fuel inlet 142 is combusted in the burner 140 to generate heat, which is used to heat one or more of the pre-reformed steam / fuel mixture flowing in the fuel cell fuel flow path 111, air flowing in the air flow path 112 (discussed below), burner fuel flowing in the burner fuel flow path 114 and water / steam flowing in the water / steam flow path 116.

[0047] As the power output of the fuel cell stack decreases, the fuel cell stack 130 may require an increase in the amount of thermal energy provided to it to maintain the temperatures necessary for efficient operation of the fuel cell stack 130. Additional thermal energy may be provided to the fuel cell stack 130 by increasing the proportion of burner fuel flowing into the burner fuel flow path 114 of the heat exchanger 110 and decreasing the proportion of burner fuel flowing into the burner fuel bypass conduit 197. The burner fuel flow path 114 preheats the burner fuel before it is provided to the burner 140. If the burner fuel is not preheated prior to entering the burner 140, the burner fuel may be at a temperature that may cause unwanted cooling in the burner 140 as the burner fuel flows into the burner 140, which may reduce the temperature of the burner 140. Preheating burner fuel in the burner fuel flow path 114 increases the temperature of the burner fuel before it enters the burner 140, which may reduce the likelihood or extent of any unwanted cooling in the burner 140 resulting from the burner fuel flowing into the burner 140.

[0048] Increasing the proportion of burner fuel flowing into the burner fuel flow path 114 of the heat exchanger 110 and decreasing the proportion of burner fuel flowing into the burner fuel bypass conduit 197 will result in increasing the temperature of the burner fuel supplied to the burner 140. Increasing the temperature of the burner fuel supplied to the burner 140 increases the thermal energy provided to the burner 140, which may result in an increase of the exhaust gas temperature of the burner 140. This in turn may result in the air temperature flowing out of the air flow path 112 of the heat exchanger 110 and into the fuel cell stack 130 increasing, thereby increasing the amount of thermal energy provided to the fuel cell stack 130, which will result in the temperature of the fuel cell stack 130 increasing. Accordingly, increasing the flow rate of burner fuel flowing through the fuel flow path 114 of the heat exchanger 110 and decreasing the flow rate of burner fuel flowing through the burner fuel bypass conduit 197 (e.g. by closing the burner fuelbypass conduit 197) may increase the thermal efficiency of the fuel cell system 100 as the power output of the fuel cell stack 130 decreases.

[0049] As the power output of the fuel cell stack 130 increases, the fuel cell stack 130 may require a reduction in the thermal energy provided to it to maintain the temperatures necessary for efficient operation of the fuel cell stack 130. The amount of thermal energy provided to the fuel cell stack 130 may be reduced by decreasing the proportion of burner fuel flowing into the burner fuel flow path 114 of the heat exchanger 110 and increasing the proportion of burner fuel flowing into the burner fuel bypass conduit 197. Increasing the flow rate of burner fuel flowing through the burner fuel bypass conduit 197 and, therefore, reducing the flow rate of burner fuel flowing through the burner fuel flow path 114 of the heat exchanger 110, reduces the temperature of the burner fuel supplied to the burner 140 via the burner fuel conduit 183. Reducing the temperature of the burner fuel supplied to the burner 140 reduces the amount of thermal energy provided to the burner 140, which may result in a reduction of the exhaust gas temperature of the burner 140. This in turn may result in the air temperature flowing out of the air flow path 112 of the heat exchanger 110 and into the fuel cell stack 130 decreasing, thereby reducing the amount of thermal energy provided to the fuel cell stack 130, which will result in the temperature of the fuel cell stack 130 reducing.

[0050] The flow rate of burner fuel flowing into and through the burner fuel flow path 114 of the heat exchanger 110 and burner fuel bypass conduit 197 may adjusted by, for example, controlling a valve associated with the burner fuel bypass conduit 197. For example, the flow rate of burner fuel flowing into and through the burner fuel bypass conduit 197 may be increased and decreased in order to decrease and increase the amount of thermal energy provided to the fuel cell stack 130, respectively.

[0051] A portion of the burner fuel (which comprises hydrogen) flowing in the burner fuel conduit 182 may be selectively directed into the recirculation conduit 184 and thus to the steam venturi 153. The burner fuel in the recirculation conduit 184 may then be drawn into the pre-reformer 150 through the steam venturi 153 as discussed above. The recirculation conduit 184 therefore allows hydrogen in the burner fuel that was not oxidised in the fuel cell stack 130 to be recirculated through the fuel cell stack 130. Thisrecirculation allows the fuel utilisation of the fuel cell stack 130 to remain at a preferred level (75-85%) but increase the fuel utilisation of the fuel cell system 100. This is because unreacted fuel flowing out of the fuel cell stack 130 can be recirculated through the fuel cell stack 130 to be reacted in the fuel cell stack 130. The flow rate of burner fuel directed from the burner fuel conduit 182 into the recirculation conduit 184 may be controlled by a valve or any other suitable device (e.g. a fixed pressure drop) associated with the recirculation conduit 184.

[0052] The exhaust gas generated from combusting the burner fuel in the burner 140 exits the burner 140 through the exhaust outlet 144 of the burner 140 and flows into the exhaust gas conduit 191. Exhaust gas flowing in the exhaust gas conduit 191 flows into the exhaust gas flow path 113 of the heat exchanger 110 through the exhaust gas inlet 121. As exhaust gas flows through the exhaust gas flow path 113, the heat from the exhaust gas is used to heat one or more of the pre-reformed steam / fuel mixture flowing in the fuel cell fuel flow path 111, air flowing in the air flow path 112 (discussed below), burner fuel flowing in the burner fuel flow path 114 and water / steam flowing in the water / steam flow path 116. The exhaust gas is cooled as it flows through the heat exchanger 110 (via the exhaust gas flow path 113). The cooled exhaust gas exits the exhaust gas flow path 113 through the exhaust gas outlet 122 and flows into the exhaust gas conduit 192.

[0053] The cooled exhaust gas flowing in the exhaust gas conduit 192 flows into the WHR exhaust gas flow path 173 of the WHR heat exchanger 170 through the WHR gas inlet 171. As the exhaust gas flows through the WHR exhaust gas flow path 173, the heat from the cooled exhaust gas is used to heat water flowing in the water flow path 176. The water heated in the water flow path 176 by the exhaust gas flowing in the WHR exhaust gas flow path 173 may exit the WHR heat exchanger 170 through the outlet 175 as heated water or steam depending on the temperature and flow rate of the exhaust gas through the WHR exhaust gas flow path 173 and the flow rate of water through the water flow path 176. The heated water or steam may then be used for any suitable heating purposes (e.g. hot water for showering, swimming pool heating, hydronic heating systems, small industrial heating purposes). As the exhaust gas flows through the WHR exhaust gas flow path 173 it is further cooled and flows out of the WHR exhaust gas flow path 173 through the WHR gas outlet 172, where the exhaust gas may be released to atmosphere. Theexhaust gas may contain water vapour, which may condense as the exhaust gas flows through the exhaust gas flow path 173. This condensed water vapour may be recovered and drained out of the WHR heat-exchanger 170 via a condensed water outlet (not shown) in the WHR heat-exchanger 170. The condensed water vapour that is drained out of the WHR heat-exchanger 170 may be used as process water by being fed into the water inlet 127 of the heat-exchanger 110. The recovered water may be used to supplement process water provided by the source of water 194. Further, the recovered water may be treated (e.g. to remove particulates and / or contaminants) before being fed into the water inlet 127 of the heat-exchanger 110.

[0054] During shut down of the natural gas fuel cell system 100, the exhaust gas bypass conduit 193 may be opened (e.g. by way of a valve) so that exhaust gas flowing in the exhaust gas conduit 191 bypasses the exhaust gas flow path 113 of the heat exchanger 110 and flows directly to the WHR heat exchanger 170 via the exhaust gas bypass conduit 193 and the exhaust gas conduit 192. This prevents the exhaust gas from providing heat to the heat exchanger 110, which may assist in more rapid cooling of the heat exchanger 110 during shut down of the natural gas fuel cell system 100. During normal operation, the exhaust gas bypass conduit 193 may be closed (e.g. by way of a valve) so that all exhaust gas from the burner 140 is directed through the exhaust gas flow path 113 of the heat exchanger 110.

[0055] Alternatively or additionally the exhaust gas bypass conduit 193 may be utilised during operation of the fuel cell system 100 (i.e. not during shut down) to provide higher grade waste heat to the WHR heat exchanger 170. For example, if heated water or steam at a higher temperature is required to be output from the WHR heat exchanger 170, the exhaust gas bypass conduit 193 may be selectively opened to allow some or all of the exhaust gas flowing in the exhaust gas conduit 191 to bypass the exhaust gas flow path 113 of the heat exchanger 110 and flow directly to the WHR heat exchanger 170 via the exhaust gas bypass conduit 193 and the exhaust gas conduit 192. Further, if exhaust gas from the burner 140 is providing more heat to the heat exchanger 110 than is required, at least a portion of the exhaust gas may be directed into the exhaust gas bypass conduit 193. The flow rate of exhaust gas directed from the exhaust gas conduit 191 into the exhaust gas bypass conduit 193 may be controlled by a valve or any other suitable device arranged tocontrol the flow rate of exhaust gas flowing into the exhaust gas bypass conduit 193 from the exhaust gas conduit 191.

[0056] Air from the source of air 185 (e.g. filtered or unfiltered ambient air) flows into and through the process air conduit 186. Air flowing in the process air conduit 186 flows into the air flow path 112 of the heat exchanger 110 through the air inlet 119. As air flows through the air flow path 112, it is heated by heat provided by anode-off-gas flowing through the anode-off-gas flow path 115 and / or by heat provided by exhaust gas flowing through the exhaust gas flow path 113. The heated air flows out of the air flow path 112 through the air outlet 120 and into the air conduit 187.

[0057] The heated air flowing in the air conduit 187 flows into the fuel cell stack 130 through the air inlet 133. The heated air flowing into the fuel cell stack 130 through the air inlet 133 is provided to the cathode of the fuel cell(s) of the fuel cell stack 130. It will be appreciated that the heated air provides oxygen to the cathode of the fuel cell(s) of the fuel cell stack 130 for the fuel cell reaction.

[0058] After flowing past the cathode of the fuel cell(s) of the fuel cell stack 130, the air exits the fuel cell stack 130 through the air outlet 134 and flows into the burner air inlet conduit 188. It will be appreciated that as air flows past the cathodes of the fuel cell(s) of the fuel cell stack 130), the air is depleted of oxygen because oxygen in the air is utilised in the fuel cell reaction. Accordingly, air flowing out of the air outlet 134 will have a lower oxygen content compared to air flowing into the air inlet 133. However, air flowing out of the air outlet 134 will still comprise oxygen as not all the oxygen in the air flowing into the air inlet 133 will be utilised in the fuel cell reaction in the fuel cell stack 130. Air flowing in the burner air inlet conduit 188 flows into the burner 140 through the air inlet 141. The air entering the burner 140 through the air inlet 141 is used to combust the burner fuel flowing into the burner 140 through the fuel inlet 142.

[0059] Air from the source of air (e.g. ambient air) may flow through the cooling air conduit 189 and into the burner 140 through the cooling air inlet 143. The air flowing into the burner 140 through the cooling air inlet 143 may be used for cooling the burner 140.

[0060] Air may be selectively drawn from the process air conduit 186 into and through the cooling air bypass conduit 190. Air drawn into the cooling air bypass conduit 190 bypasses the air flow path 112 of the heat exchanger 110 and flows into the fuel cell stack 130 through the air inlet 133 via the cooling air bypass conduit 190 and the air conduit 187. The flow rate of cooling air provided to the fuel cell stack 130 via the cooling air bypass conduit 190 may vary depending on the amount of cooling required by the fuel cell stack 130. The amount of cooling air provided to the fuel cell stack 130 via the cooling air bypass conduit 190 may be controlled, for example, by way of a valve (not shown) associated with the cooling air bypass conduit 190 or any other suitable device arranged to control the flow rate of air flowing into and through the cooling air bypass conduit 190.

[0061] It will be appreciated from the above that the anode-off-gas flowing through the anode-off-gas flow path 115 and the exhaust gas flowing through the exhaust gas flow path 113 both act as heating streams for the heat exchanger 110. The heat exchanger 110 thus comprises two heating streams that are each configured to heat one or more of the prereformed steam / fuel mixture flowing in the fuel cell fuel flow path 111, air flowing in the air flow path 112, burner fuel flowing in the burner fuel flow path 115, and water / steam flowing in the water / steam flow path 116 of the heat exchanger 110.

[0062] As can be seen from Figure 1, the heating streams enter the heat exchanger 110 from a first side 109 of the heat exchanger 110, while the steams that are to be heated by the heating streams enter the heat exchanger 110 from, or proximate to, an opposite, second side 129 of the heat exchanger 110. The streams that are to be heated by the heating streams include the pre-reformed steam / fuel mixture flowing in the fuel cell fuel flow path 111, air flowing in the air flow path 112, burner fuel flowing in the burner fuel flow path 115 and water / steam flowing in the water / steam flow path 116 of the heat exchanger 110. Accordingly, the heat exchanger 110 operates in predominantly a counter flow arrangement, where the heating streams flow in the opposite direction through the heat exchanger 110 compared to the streams that are to be heated. It will be appreciated that there may be some crossflow heat exchange occurring in the heat exchanger 110 (e.g. at the plenums of the heat exchanger 110).

[0063] As diagrammatically represented in Figure 1, the fuel inlet 117 of the heat exchanger 110 is positioned downstream of the inlet of the other streams that are to be heated by the heating streams. This is because the pre-reformed steam / fuel mixture flowing in the fuel conduit 178 may require less heating than the other streams that are to be heated in order to exit the heat exchanger 110 at the desired temperature (e.g. 650°C-700°C), given the pre-reformed steam / fuel mixture flowing in the fuel conduit 178 may enter the heat exchanger 110 at a higher temperature (e.g. 300°C-400°C, preferably 350°C-400°C) compared to the other streams that are to be heated. Introducing the pre-reformed steam / fuel mixture into the heat exchanger 110 in this way exposes the stream to less heat during passage through the heat exchanger 110 than the other streams that are to be heated. However, the fuel inlet 117 may be located at a particular position along the heat exchanger 110 where, during operation, the temperature inside the heat exchanger 110 is approximately equal to the temperature of the pre-reformed steam / fuel mixture entering the heat exchanger 110 through the fuel inlet 117. This may avoid the pre-reformed steam / fuel mixture entering a zone of the heat exchanger 110 that is cooler than the pre-reformed steam / fuel mixture, thereby avoiding unnecessary cooling of the pre-reformed steam / fuel mixture before it is again heated as it flows through the heat exchanger 110.

[0064] Although the fuel cell system 100 has been described above for use with natural gas supplied by the source of natural gas 154, it will be appreciated that the source of natural gas could be replaced with a source of hydrogen. In such an embodiment, the prereformer 150 may be omitted or not utilised. If the pre-reformer 150 is omitted, the steam conduit 195 may be directly coupled in fluid communication to the inlet 117 of the heat exchanger 110. Further, in this embodiment, given no internal reforming of natural gas would occur in the fuel cell stack 130, which would provide cooling to the fuel cell stack 130, further cooling may be provided to the fuel cell stack 130 by the cooling air bypass conduit 190.

[0065] Further, although the fuel cell system 100 has been describes and illustrated above for use with natural gas suppled by the source of natural gas 154, it will be appreciated that the source of natural gas may be replaced with another source of fuel (e.g. liquid petroleum gas, ethane, propane, butane, pentane, methanol).

[0066] Figure 2 is an exemplary schematic of the layout of the heat exchanger 110 showing the fuel cell fuel flow path 111, the air flow path 112, the exhaust gas flow path 113, the burner fuel flow path 114, the anode-off-gas flow path 115, and the water / steam flow path 116 through the heat exchanger 110.

[0067] As can be seen from Figure 2, exhaust gas flowing through the exhaust gas flow path 113 is configured to heat water / steam flowing through the water / steam flow path 116, air flowing through the air flow path 112, and fuel flow flowing through the fuel cell fuel flow path 111. As can also be seen from Figure 2, anode-off-gas flowing through the anode-off-gas flow path 115 is configured to heat fuel flowing through the fuel cell flow path 111 and burner fuel flowing through the burner fuel flow path 114.

[0068] The exhaust gas from the burner 140 will typically have a higher energy content than the anode-off-gas from the fuel cell stack 130. The air flowing in the air flow path 112 and water / steam flowing in the steam flow path 116 may require more heating compared to the other streams. Accordingly, air flowing in the air flow path 112 and water / steam flowing in the steam flow path 116 are exposed to (i.e. heated by) the exhaust gas flowing through the exhaust gas flow path 113. The other streams that may require less heating may be heated by only the anode-off-gas flowing in the anode-off-gas flow path 115 or a combination of exhaust gas flowing through the exhaust gas flow path 113 and anode-off-gas flowing in the anode-off-gas flow path 115

[0069] It will however be appreciated that Figure 2 is only an example of a layout of the heat exchanger 110 and that other layouts may be possible. For example, the heat exchanger 110 may be configured such that:• fuel flowing through the fuel cell fuel flow path Ill is configured to be heated by exhaust gas flowing through the exhaust gas 113 flow path and / or anode-off-gas flowing through the anode-off-gas flow path 115;• air flowing through the air flow path 112 is configured to be heated by exhaust gas flowing through the exhaust gas flow path 113 and / or anode-off-gas flowing through the anode-off-gas flow path 115;• burner fuel flowing through the burner fuel flow path 114 is configured to be heated by exhaust gas flowing through the exhaust gas flow path 113 and / or by anode-off- gas flowing through the anode-off-gas flow path 115; and• water flowing through the water / steam flow path 116 is configured to be heated by exhaust gas flowing through the exhaust gas flow path 113 and / or by anode-off-gas flowing through the anode-off-gas flow path 115.

[0070] The layout of the heat exchanger 110 may vary depending on one or more operational characteristics required of the heat exchanger 110 (e.g. heat exchanger efficiency, pressure drop, and / or exit temperature requirements of the heat exchanger 110).

[0071] Figure 3 is a schematic diagram of a hydrogen fuel cell system 200 according to another embodiment of the present disclosure. The hydrogen fuel cell system 200 is similar to the natural gas fuel cell system 100 but the heat exchanger 210 of the hydrogen fuel cell system 200 omits the water / steam flow path 116 of the heat exchanger 110 of the natural gas fuel cell system 100. The hydrogen fuel cell system 200 also omits the pre-reformer 150 of the natural gas fuel cell system 100. Instead of the source of natural gas 154 of the natural gas fuel cell system 100, the fuel inlet 217 of the heat exchanger 210 of the hydrogen fuel cell system 200 is in fluid communication with a source of hydrogen 254. Further, the hydrogen fuel cell system 200 includes a hydrogen venturi 253 in place of the steam venturi 153 of the natural gas fuel cell system 100.

[0072] Features of the hydrogen fuel cell system 200 that are identical or equivalent to those of the natural gas fuel cell system 100 are indicated with reference numerals that are equivalent to those of the natural gas fuel cell system 100 but incremented by 100. For features that are identical between the natural gas fuel cell system 100 and the hydrogen fuel cell system 200, it will be appreciated that the above description of these features in relation to the natural gas fuel cell system 100 is also applicable to the corresponding equivalent features of the hydrogen fuel cell system 200. Accordingly, the features that are common between the two systems that have been described above in relation to the natural gas fuel cell system 100 are not described again below in relation to the hydrogen fuel cell system 200.

[0073] Operation of the hydrogen fuel cell system 200 is described below.

[0074] Operation of the hydrogen fuel cell system 200 is similar to the operation of the natural gas fuel cell system 100, apart from the flow of hydrogen from the source of hydrogen 254 to the fuel cell stack 230 in the hydrogen fuel cell system 200 instead of the flow of natural gas from the source of natural gas 154 to the fuel cell stack 130 in the natural gas fuel cell system 100. Further, the hydrogen venturi 253 of the hydrogen fuel cell system 200 differs in operation to the steam venturi 153 of the natural gas fuel cell system 100. Otherwise, the hydrogen fuel cell system 200 operates in a similar manner to the natural gas fuel cell system 100. Operation of the components of the hydrogen fuel cell system 200 that are equivalent to components of the natural gas fuel cell system 100 will not be described below, as such operation has already been described above with respect to the equivalent components of the natural gas fuel cell system 100. Accordingly, only the differences in operation between the hydrogen fuel cell system 200 and the natural gas fuel cell system 100 will be described below.

[0075] The source of hydrogen 254 is coupled in fluid communication with the fuel conduit 278. Hydrogen from the source of hydrogen 254 flows into and through the fuel conduit 278 and into the fuel flow path 211 of the heat exchanger 210 through the fuel inlet 217. The hydrogen venturi 253 is in fluid communication with the fuel conduit 278.Hydrogen flowing through the fuel conduit 278 and past the hydrogen venturi 253 draws burner fuel (comprising hydrogen) in the recirculation conduit 284 through the hydrogen venturi 253 into the fuel conduit 278.

[0076] The hydrogen flowing in the fuel conduit 278 flows into the fuel cell fuel flow path 211 of the heat exchanger 210 through the fuel inlet 217. As the hydrogen flows through the fuel cell fuel flow path 211, it is heated by anode-off-gas flowing through the anode-off-gas flow path 215 and by exhaust gas flowing through the exhaust gas flow path 213. The heated hydrogen exits the fuel flow path 211 through the fuel outlet 218 and flows into the fuel conduit 279.

[0077] The heated hydrogen flowing in the fuel conduit 279 flows into the fuel cell stack 230 through the fuel inlet 231. The heated hydrogen flowing into the fuel cell stack 230 through the fuel inlet 231 is provided to the anode of the fuel cell(s) of the fuel cell stack 230 for the fuel cell reaction. It will be appreciated that, as part of the fuel cellreaction, water is generated at the anode of the fuel cell(s) of the fuel cell stack 230. It will also be appreciated that not all the hydrogen provided to the anode of the fuel cell(s) of the fuel cell stack 230 is used in the fuel cell reaction. Accordingly, flowing out of the anode-off-gas outlet 232 of the fuel cell stack 230 and into the anode-off-gas conduit 280 is a mixture of hydrogen gas and water (in the form of steam).

[0078] Reforming natural gas to produce hydrogen requires steam. Given the fuel cell stack 230 is supplied with hydrogen, there is no need to reform natural gas to produce hydrogen and, therefore, no need to supply steam. There is thus no need for the heat exchanger 210 to generate steam for this purpose. Accordingly, the heat exchanger 210 of the hydrogen fuel cell system 200 may omit the water / steam flow path 116 of the heat exchanger 110 of the natural gas fuel cell system 100.

[0079] Similar to the operation of the natural gas fuel cell system 100, a portion of burner fuel flowing in the burner fuel conduit 282 may be directed into the recirculation conduit 284. Burner fuel flowing in the recirculation conduit 284 flows to the hydrogen venturi 253, through which burner fuel in the recirculation conduit 284 is drawn into the fuel conduit 278 as hydrogen from the source of hydrogen 254 flows through the fuel conduit 278 and past the hydrogen venturi 253.

[0080] The cooling air bypass conduit 290 may be opened to provide cooling air to the fuel cell stack 230. The amount of cooling air provided to the fuel cell stack 230 via the cooling air bypass conduit 290 may vary depending on the amount of cooling required by the fuel cell stack 230. The amount of cooing air provided to the fuel cell stack 230 via the cooling air bypass conduit 290 may be controlled, for example by a valve associated with the cooling air bypass conduit 290 or any other suitable device that can control the flow rate of air flowing through the cooling air bypass conduit 290.

[0081] Given the fuel cell stack 230 is supplied with hydrogen, internal reforming of natural gas does not occur in the fuel cell stack 230. As the endothermic reaction of internal reforming does not occur in the fuel cell stack 230, the fuel cell stack 230 may require additional cooling, which may be provided by cooling air supplied via the cooling air bypass conduit 290. Alternatively, or additionally, further cooling air may be provideby increasing the volume of air flowing through the air flow path 212 of the heat exchanger 210.

[0082] As can be seen from Figure 3, unlike the inlet 117 of the heat exchanger 110, the inlet 217 of the heat exchanger 210 is not positioned downstream of the inlets of the other streams that are to be heated by the heating streams. This is because hydrogen from the source of hydrogen 254 entering the heat exchanger 210 through inlet 217 will likely have a lower temperature compared to the pre-reformed steam / fuel mixture flowing into the inlet 117 of the heat exchanger 110. However, similar to that described above with respect to the inlet 117 of the heat exchanger 110, the inlet 217 of the heat exchanger 210 may be positioned downstream of the inlets of the other streams that are to be heated by the heating streams. The inlet 217 may be located at a particular position along the heat exchanger 210 where, during operation, the temperature inside the heat exchanger 210 is approximately equal to the temperature of the hydrogen entering the heat exchanger 210 through the inlet 217.

[0083] In some embodiments, the heat exchanger 110, 210 may not include the burner fuel flow path 114, 214. In such embodiments, apart from any burner fuel being directed into the recirculation conduit 184, 284, burner fuel flowing out of the anode-off-gas heat exchanger 160, 260 may flow directly to the fuel inlet 142, 242 of the burner 140, 240.

[0084] In some embodiments, the fuel cell system 100, 200 may omit the recirculation conduit 184, 284. In such embodiments, all the burner fuel flowing out of the anode-off-gas heat exchanger 160, 260 will flow to the fuel inlet 142, 242 of the burner 140, 240 (e.g. directly or via the burner fuel flow path 114, 214 of the heat exchanger 110, 210).

[0085] In some embodiments, the fuel cell system 100, 200 may omit the exhaust gas bypass conduit 193, 293. In such embodiments, the exhaust gas from the burner 140, 240 will not bypass the heat exchanger 110, 210 and will therefore flow through the exhaust gas flow path 113, 213 of the heat exchanger 110, 210.

[0086] In some embodiments, the fuel cell system 100, 200 may omit the WHR heat exchanger 170, 270. In such embodiments, the exhaust gas flowing out of the heat exchanger 110, 210 may be released to atmosphere.

[0087] In some embodiments, the fuel cell system 100, 200 may omit the anode-off-gas heat exchanger 160, 260. In such embodiments, anode-off-gas flowing out of the anode-off gas flow path 115, 215 of the heat exchanger 110, 210 may flow directly to the fuel inlet 142, 242 of the burner 140, 240 and / or a portion of anode-off-gas flowing out of the anode-off gas flow path 115, 215 of the heat exchanger 110, 210 may be directed into the recirculation conduit 184,284 (if present).

[0088] In some embodiments, the heat exchanger 110 may omit the water / steam flow path 116. In such embodiments, a source of steam may be coupled in fluid communication to the inlet 151 of the pre-reformer 150. The source of steam may be coupled in fluid communication to the inlet 151 so as to draw natural gas into the pre-reformer 150 through the steam venturi 153 from the source of natural gas 154 and burner fuel (comprising hydrogen) into the pre-reformer 150 through the steam venturi 153 from the recirculation conduit 184 (if present) as discussed above.

[0089] In some embodiments, the fuel cell system 100, 200 may omit the cooling air bypass conduit 190, 290 and / or the cooling air conduit 189, 289. In such embodiments, cooling for the fuel cell stack 130, 230 and / or the burner 140, 240 may be provided by any other suitable cooling means.

[0090] In some embodiments, the natural gas fuel cell system 100 may omit the prereformer 150. In such embodiments, steam flowing in the steam conduit 195 flows past the steam venturi 153, which causes natural gas from the source of natural gas 153 and burner fuel in the recirculation conduit 184 (if present) to be drawn into the steam conduit 195 through the steam venturi 153 to be mixed with the steam to create a steam / fuel mixture. This steam / fuel mixture flows to the fuel inlet 117 of the fuel cell fuel flow path 111 of the heat exchanger 110. In such embodiments, higher hydrocarbons may be present in the steam / fuel mixture and these higher hydrocarbons may cause coking in the heat exchanger 110 when the steam / fuel mixture is heated in the heat exchanger 110. Accordingly, including the pre-reformer 150 in the natural gas fuel cell system 100 may reduce the amount of higher hydrocarbons entering the heat exchanger 110 and, therefore, the amount of coking in the heat exchanger 100 caused by heating higher hydrocarbons.

[0091] Although the fuel cell system 100 has been described as having a steam venturi 153, it will be appreciated that the steam venturi 153 may be replaced with a blower.Similarly, the venturi 253 of the fuel cell system 200 may be replaced with a blower.

[0092] Although the fuel cell systems 100, 200 have been described and illustrated as having a burner 140, 240, it will be appreciated that the burner 140, 240 may be replaced with any suitable alternate heating source (e.g. an electric heater). In such an embodiment, conduit 188, 288 may be coupled in fluid communication with the inlet 121, 221 of the heat exchanger 110, 210 and exhaust gas conduit 191, 291 may be omitted. Accordingly, in this embodiment, gases flowing into the inlet 121, 221 of the heat exchanger 110, 210 (via the fuel cell stack 130, 230) would be sufficiently heated by the heating source so that they can provide heat to one or more of the other gases flowing through the heat exchanger 110, 210 in a similar manner to that described above with respect to the exhaust gases flowing through the heat exchanger 110, 210. In such an embodiment, such a heating source may be upstream (e.g. associated with conduit 187, 287) or downstream (e.g. associated with conduit 188, 288) of the fuel cell stack 130, 230. Alternatively, the burner 140, 240 may be replaced with two suitable alternate heating sources, one upstream (e.g. associated with conduit 187, 287) of the fuel cell stack 130, 230 and the other downstream (e.g. associated with conduit 188, 288) of the fuel cell stack 130, 230. Further, in this embodiment, no burner fuel would be directed to and through the burner fuel flow path 114, 214 and then subsequently to the burner 140, 240. Instead, burner fuel flowing in the conduit 182, 282 would be directed to the recirculation conduit 184, 284.

[0093] Figure 4 illustrates an electrolyser system 300 according to an embodiment of the present disclosure. The electrolyser system 300 includes a heat exchanger 310, an electrolyser stack 330, a burner 340, a hydrogen / steam heat exchanger 360, and a waste-heat-recovery (WHR) heat exchanger 370.

[0094] The heat exchanger 310 defines a steam / hydrogen flow path 311, an air flow path 312, an exhaust gas flow path 313, a burner fuel flow path 314, an hydrogen gas flow path 315 and a water / steam flow path 316. The steam / hydrogen flow path 311 includes a steam / hydrogen inlet 317 and a steam / hydrogen outlet 318. The air flow path 312 includes an air inlet 319 and an air outlet 320. The exhaust gas flow path 313 includes an exhaustgas inlet 321 and an exhaust gas outlet 322. The burner fuel flow path 314 includes a burner fuel inlet 323 and a burner fuel outlet 324. The hydrogen gas flow path 315 includes an hydrogen gas inlet 325 and an hydrogen gas outlet 326. The water / steam flow path 116 includes a water inlet 327 and a steam outlet 328.

[0095] As Figure 4 illustrates, the flow direction of the exhaust gas flow path 313 and the hydrogen gas flow path 315 through the heat exchanger 310 is opposite to that of the steam / hydrogen flow path 311, air flow path 312, burner fuel flow path 314 and water / steam flow path 316. The gas streams following the exhaust gas flow path 313 and hydrogen gas flow path 315 are heating streams configured to provide heat to the gas streams following the hydrogen / steam flow path 311, air flow path 312, burner fuel flow path 314 and water / steam flow path 316. Accordingly, the heat exchanger 310 operates in a predominantly counter flow arrangement, where the heating streams flow in the opposite direction through the heat exchanger 310 compared to the streams that are to be heated. It will be appreciated that there may be some crossflow heat exchange occurring in the heat exchanger 310 (e.g. at the plenums of the heat exchanger 310).

[0096] The electrolyser stack 330 comprises one or more electrolytic cells, such as solid oxide electrolytic cells. The electrolyser stack 330 includes a steam / hydrogen inlet 331, a hydrogen outlet 332, an air inlet 333, and an air outlet 334. Steam / hydrogen inlet 331 is arranged to provide water (in the form of steam) to the cathode of the electrolytic cells of the electrolyser stack 330, while the air inlet 333 is arranged to provide air to the anode of the electrolytic cells of the electrolyser stack 330.

[0097] The burner 340 is configured to combust fuel to generate heat, which is used to heat steam and air in the heat exchanger 310 to a required temperature (discussed below) before flowing into the electrolyser stack 330. The required temperature of the air and steam flowing into the electrolyser stack 330 may be dependent on the type of electrolytic cells used in the electrolyser stack 330. The burner 340 includes an air inlet 341, a fuel inlet 342, and an exhaust outlet 344. The burner 340 also includes a spark rod 345 for igniting fuel to start the burner 340. The heat generated by the burner 340 may also be used to heat other streams flowing thought the heat exchanger 310 (discussed below).

[0098] The hydrogen / steam heat exchanger 360 includes a hydrogen gas inlet 361, a hydrogen gas outlet 362, and a hydrogen flow path 363 extending through the hydrogen / steam heat exchanger 360 between the hydrogen gas inlet 361 and the hydrogen gas outlet 362. The hydrogen / steam heat exchanger 360 also includes a cooling water inlet 364, a cooling water outlet 365 and a cooling water flow path 366 extending through the hydrogen / steam heat exchanger 360 between the cooling water inlet 364 and the cooling water outlet 365. The cooling water inlet 364 is coupled in fluid communication with a source of cooling water 367, which may be mains water or any suitable source of water. Water flowing out of the cooling water outlet 365 may be appropriately discharged or may be cooled by any suitable cooling systems before being returned to the cooling water inlet 364. Alternatively, or additionally, heated water flowing out of the cooling water outlet 365 may be used for other suitable heating purposes (e.g. hot water for showering, swimming pool heating, hydronic heating systems, small industrial heating purposes).

[0099] The WHR heat exchanger 370 includes a WHR gas inlet 371, a WHR gas outlet 372 and a WHR exhaust gas flow path 373 extending through the WHR heat exchanger 370 between the WHR gas inlet 371 and the WHR gas outlet 372. The WHR heat exchanger 370 also includes a water inlet 374, a water outlet 375 and a water flow path 376 extending through the WHR exchanger 370 between the water inlet 374 and the water outlet 375. The water inlet 374 is coupled in fluid communication with a suitable source of water 377 (such as mains water). Water flowing out of the water outlet 375 may be used for any suitable heating purposes (e.g. hot water for showering, swimming pool heating, hydronic heating systems, small industrial heating purposes), after which it may be returned to the water inlet 374 (e.g. via a storage tank) or appropriately discarded.

[0100] The steam / hydrogen inlet 317 of the heat exchanger 310 is coupled in fluid communication with the steam outlet 328 of the heat exchanger 310 by a steam conduit 378. The steam / hydrogen outlet 318 of the heat exchanger 310 is coupled in fluid communication with the steam / hydrogen inlet 331 of the electrolyser stack 330 by a steam / hydrogen conduit 379. The hydrogen gas outlet 332 of the electrolyser stack 330 is coupled in fluid communication with the hydrogen gas inlet 325 of the heat exchanger 310 by a hydrogen gas conduit 380. The hydrogen gas outlet 326 of the heat exchanger 310 is coupled in fluid communication with the hydrogen gas inlet 361 of the hydrogen / steamheat exchanger 360 by a hydrogen gas conduit 381. The hydrogen gas outlet 362 of the hydrogen / steam heat exchanger 360 is coupled in fluid communication with the burner fuel inlet 323 of the heat exchanger 310 by a hydrogen gas conduit 382. The burner fuel outlet 324 of the heat exchanger 310 is coupled in fluid communication with the fuel inlet 342 of the burner 340 by a burner fuel conduit 383.

[0101] The hydrogen gas conduit 382 is coupled in fluid communication with a steam venturi 353 by a recirculation conduit 384. The recirculation conduit 384 allows hydrogen flowing in the hydrogen gas conduit 382 to flow to the steam venturi 353. The flow rate of fuel flowing into the recirculation conduit 384 from the hydrogen gas conduit 382 may be controlled by any suitable means (e.g. a valve) associated with the recirculation conduit 384.

[0102] Branching off the hydrogen gas conduit 382 is a hydrogen collection conduit 396. The hydrogen collection conduit 396 allows for hydrogen produced by the electrolyser stack 330 to be collected. The collected hydrogen may be processed (e.g. to remove any remaining steam) before being stored. The collected hydrogen may be stored and used later for other purposes (e.g. ammonia and methanol production, energy carrier for use in fuel cell vehicles or fuel cell electricity generation). The flow rate of hydrogen flowing into the hydrogen collection conduit 396 from the hydrogen gas conduit 382 may be controlled by any suitable means (e.g. a valve).

[0103] The air inlet 319 of the heat exchanger 310 is in fluid communication with a source of air 385 via a process air conduit 386. The air outlet 320 of the heat exchanger 310 is coupled in fluid communication with the air inlet 333 of the electrolyser stack 330 by a air conduit 387. The air outlet 334 of the electrolyser stack 330 is coupled in fluid communication with the air inlet 341 of the burner 340 by a burner air inlet conduit 388.

[0104] The exhaust outlet 344 of the burner 340 is coupled in fluid communication with the exhaust gas inlet 321 of the heat exchanger 310 by an exhaust gas conduit 391. The exhaust gas outlet 322 of the heat exchanger 310 is coupled in fluid communication with the WHR gas inlet 371 of the WHR heat exchanger 370 by a exhaust gas conduit 392.

[0105] The water inlet 327 of the heat exchanger 310 is in fluid communication with a source of water 394 (e.g. mains water, deionised water, or any other suitable source of water). The steam venturi 353 is in fluid communication with the steam conduit 378. The steam venturi 353 is configured such that steam flowing in the steam conduit 378 to the inlet 317 of the heat exchanger 310 draws hydrogen gas from the recirculation conduit 384 into the steam conduit 378 through the steam venturi 353.

[0106] Operation of the electrolyser system 300 will be described below.

[0107] Water flows from the source of water 394 into the water / steam flow path 316 of the heat exchanger 310 through the water inlet 326. As the water flows through the water / steam flow path 316, the water is converted to steam by heat provided by hydrogen gas flowing in the hydrogen gas flow path 315 (discussed below) and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 313 (discussed below). The steam exits the water / steam flow path 316 through the steam outlet 328 and flows into and through the steam conduit 378. Steam flows through the steam conduit 378 to the inlet 317 of the heat exchanger 310.

[0108] Steam flowing through the steam conduit 378 past the steam venturi 353 causes hydrogen in the recirculation conduit 384 to be drawn into the steam conduit 378 through the steam venturi 353. The steam and any hydrogen from the recirculation conduit 384 drawn into the steam conduit 378 through the steam venturi 353 form a steam / hydrogen mixture. The steam / hydrogen mixture flows into the heat exchanger 310 through the inlet 317, where it flows through the steam / hydrogen flow path 311 of the heat exchanger 310.

[0109] The steam / hydrogen mixture is heated as it flows through the steam / hydrogen flow path 311 by heat provided by hydrogen gas flowing in the hydrogen gas flow path 315 (discussed below) and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 313 (discussed below). The heated steam / hydrogen mixture exits the steam / hydrogen flow path 311 through the steam / hydrogen outlet 318 and flows into the steam / hydrogen conduit 379. The heated steam / hydrogen mixture exiting the steam / hydrogen outlet 318 may have a temperature in the range 650°C-750°C, for example. However, depending on the type of electrolytic cells used in the electrolyser stack 330, the temperature range of the heated steam / hydrogen mixture exiting the steam / hydrogen outlet318 may be between 500°C-900°C. The temperature of the heated steam / hydrogen mixture exiting the steam / hydrogen outlet 318 may therefore be controlled to be at a temperature suitable for use with the particular electrolytic cells being used in the electrolyser stack 330.

[0110] The heated steam / hydrogen mixture flows through the steam / hydrogen conduit 379 and into the electrolyser stack 330 through the steam / hydrogen inlet 331.Subsequently, the heated steam / hydrogen mixture is provided to cathode of the electrolytic cells of the electrolyser stack 330. The electrolytic cells of the electrolyser stack 330 have suitable anodes, cathodes, and electrolytes / membranes to split water (in the steam) into hydrogen gas and oxygen gas. The electrolyser stack 330 is supplied with electrical power required for the electrolysis reaction via electrical circuit 335. Hydrogen gas and oxygen gas produced by the electrolysis reaction in the electrolyser stack 330 flow out of the electrolyser stack 330 via the hydrogen gas outlet 332 and air outlet 334, respectively. The hydrogen gas may also comprise water (in the form of steam).[OHl] The hydrogen gas exiting the electrolyser stack 330 through the hydrogen gas outlet 332 may have a temperature of 650°C - 750°C. However, depending on the type of electrolytic cells used in the electrolyser stack 330, the temperature of the hydrogen gas exiting the hydrogen gas outlet 332 may vary.

[0112] The hydrogen gas exiting the electrolyser stack 330 through the hydrogen gas outlet 332 flows into and through the hydrogen gas conduit 380. The hydrogen gas flowing through the hydrogen gas conduit 380 flows into the hydrogen gas flow path 315 of the heat exchanger 310 through the hydrogen gas inlet 325. As the hydrogen gas flows through the hydrogen gas flow path 315, the heat from the hydrogen gas is used to heat one or more of the steam / hydrogen mixture flowing in the hydrogen / steam flow path 311, air flowing in the air flow path 312 (discussed below), burner fuel flowing in the burner fuel flow path 314 (discussed below) and water / steam flowing in the water / steam flow path 316.

[0113] The hydrogen gas is cooled as it flows through the heat exchanger (via the hydrogen gas flow path 315). The cooled hydrogen gas exits the hydrogen gas flow path 315 through the hydrogen gas outlet 326 and flows into the hydrogen gas conduit 381. Thecooled hydrogen gas flowing in the hydrogen gas conduit 381 flows into the hydrogen flow path 363 of the hydrogen / steam heat exchanger 360 through the hydrogen gas inlet 361 of the hydrogen / steam heat exchanger 360.

[0114] Cooling water flowing through the cooling water flow path 366 of the hydrogen / steam heat exchanger 360 further cools the hydrogen gas flowing in the hydrogen flow path 363, which condenses at least a portion of any water vapour in the hydrogen gas. The condensed water vapour may then be drained away and recovered, thus reducing the moisture content of the hydrogen gas flowing out of the hydrogen flow path 363. The condensed water vapour may be drained away via a condensed water outlet (not shown) in the anode-off-gas heat-exchanger 360. The recovered water may be subsequently used for other purposes. For example, the recovered water may be treated (e.g. deionised) and then fed into the water inlet 327 of the heat exchanger 310. The hydrogen gas flows out of the hydrogen flow path 363 through the hydrogen gas outlet 362 and into the hydrogen conduit 382.

[0115] Hydrogen gas flowing in the hydrogen gas conduit 382 flows into the burner fuel flow path 314 of the heat exchanger 310 through the burner fuel inlet 323. This hydrogen gas will be referred to below as “burner fuel”. The burner fuel is heated as it flows through the burner fuel flow path 314 by heat provided by hydrogen gas flowing in the hydrogen gas flow path 315 and / or by heat provided by exhaust gas flowing in the exhaust gas flow path 313 (discussed below). The heated burner fuel exits the burner fuel flow path 314 through the burner fuel outlet 324 and flows into the hot burner fuel conduit 383.

[0116] The heated burner fuel flowing in the hot burner fuel conduit 383 flows into the burner 340 through the fuel inlet 342. The heated burner fuel flowing into the burner 340 through the fuel inlet 342 is combusted in the burner 340 to generate heat, which is used to heat one or more of the steam / hydrogen mixture flowing in the hydrogen / steam flow path 311, air flowing in the air flow path 312, burner fuel flowing in the burner fuel flow path 314 and water / steam flowing in the water / steam flow path 316.

[0117] A portion of the hydrogen gas flowing in the hydrogen gas conduit 382 may be selectively directed into the recirculation conduit 384 and thus to the steam venturi 353.The hydrogen gas in the recirculation conduit 384 may then be drawn into the steam conduit 378 through the steam venturi 353 as discussed above.

[0118] Additionally, or alternatively, a portion of the hydrogen gas flowing in the hydrogen gas conduit 382 may be selectively directed into the hydrogen collection conduit 396. Hydrogen directed into the hydrogen collection conduit 396 may subsequently be collected and stored. The collected hydrogen may be processed (e.g. to reduce the amount of any remaining steam) before being stored. The collected hydrogen may be used for other purposes (e.g. ammonia and methanol production, energy carrier for use in fuel cell vehicles or fuel cell electricity generation).

[0119] The hot exhaust gas generated from combusting hydrogen gas in the burner 340 exits the burner 340 through the exhaust outlet 344 of the burner 340 and flows into the exhaust gas conduit 391. Exhaust gas flowing in the exhaust gas conduit 391 flows into the exhaust gas flow path 313 of the heat exchanger 310 through the exhaust gas inlet 321. As exhaust gas flows through the exhaust gas flow path 313, the heat from the exhaust gas is used to heat one or more of the steam / hydrogen mixture flowing in the steam / hydrogen flow path 311, air flowing in the air flow path 312 (discussed below), burner fuel flowing in the burner fuel flow path 314 and water / steam flowing in the water / steam flow path 316. The exhaust gas is cooled as it flows through the heat exchanger 310 (via the exhaust gas flow path 313). The cooled exhaust gas exits the exhaust gas flow path 313 through the exhaust gas outlet 322 and flows into the exhaust gas conduit 392.

[0120] The cooled exhaust gas flowing in the exhaust gas conduit 392 flows into the WHR exhaust gas flow path 373 of the WHR heat exchanger 370 through the WHR gas inlet 371. As the exhaust gas flows through the WHR exhaust gas flow path 373, the heat from the cooled exhaust gas is used to heat water flowing in the water flow path 376. The water heated in the water flow path 376 by the exhaust gas flowing in the WHR exhaust gas flow path 373 may exit the WHR heat exchanger 370 through the outlet 375 as heated water or steam depending on the temperature and flow rate of the exhaust gas through the WHR exhaust gas flow path 373 and the flow rate of water through the water flow path 376. The heated water or steam may then be used for any suitable heating purposes. As the exhaust gas flows through the WHR exhaust gas flow path 373 it is further cooled andflows out of the WHR exhaust gas flow path 373 through the WHR gas outlet 372, where the exhaust gas may be released to atmosphere. The exhaust gas may contain water vapour, which may condense as the exhaust gas flows through the exhaust gas flow path 373. This condensed water vapour may be recovered and drained out of the WHR heat-exchanger 370 via a condensed water outlet (not shown) in the WHR heat-exchanger 370. The condensed water vapour that is drained out of the WHR heat-exchanger 370 may be used as process water by being fed into the water inlet 327 of the heat-exchanger 310. The recovered water may be used to supplement process water provided by the source of water 394. Further, the recovered water may be treated (e.g. to remove particulates and / or contaminants) before being fed into the water inlet 327 of the heat-exchanger 310.

[0121] Air from the source of air 385 (e.g. filtered or unfiltered ambient air) flows into and through the process air conduit 386. Air flowing in the process air conduit 386 flows into the air flow path 312 of the heat exchanger 310 through the air inlet 319. As air flows through the air flow path 312, it is heated by heat provided by hydrogen gas flowing through the hydrogen gas flow path 315 and / or by heat provided by exhaust gas flowing through the exhaust gas flow path 313. The heated air flows out of the air flow path 312 through the air outlet 320 and into the hot air conduit 387.

[0122] The heated air flowing in the air conduit 387 flows into the electrolyser stack 330 through the air inlet 333. The electrolysis reaction of splitting water into hydrogen gas and oxygen gas is endothermic. Accordingly, heat is required to maintain thermal equilibrium and, therefore, sustain this reaction. Heat required to sustain this endothermic reaction may at least be partially provided by the heated steam / hydrogen mixture flowing into the electrolyser stack 330 through steam / hydrogen inlet 331 and heated air flowing into the electrolyser stack 330 through the air inlet 333.

[0123] The oxygen gas produced by the electrolysis reaction in the electrolyser stack 330 flows out of the air outlet 334 of the electrolyser stack 330 and into the burner air inlet conduit 388. Oxygen gas flowing in the burner air inlet conduit 388 flows into the burner 340 through the air inlet 341. The oxygen gas entering the burner 340 through the air inlet 341 is used to combust the hydrogen gas flowing into the burner 340 through the fuel inlet

[0124] It will be appreciated from the above that the hydrogen gas flowing through the hydrogen gas flow path 315 and the exhaust gas flowing through the exhaust gas flow path 313 both act as heating streams for the heat exchanger 310. The heat exchanger 310 thus comprises two heating streams that are each configured to heat one or more of the steam / hydrogen mixture flowing in the steam / hydrogen flow path 311, air flowing in the air flow path 312, burner fuel flowing in the burner fuel flow path 315, and water / steam flowing in the water / steam flow path 316 of the heat exchanger 310.

[0125] As can be seen from Figure 4, the heating streams enter the heat exchanger 310 from a first side 309 of the heat exchanger 310, while the steams that are to be heated by the heating streams enter the heat exchanger 310 from, or proximate to, an opposite, second side 329 of the heat exchanger 310. The streams that are to be heated by the heating streams include the steam / hydrogen mixture flowing in the steam / hydrogen flow path 311, air flowing in the air flow path 312, burner fuel flowing in the burner fuel flow path 315 and water / steam flowing in the water / steam flow path 316 of the heat exchanger 310.

[0126] As diagrammatically represented in Figure 4, the steam / hydrogen inlet 317 of the heat exchanger 310 is positioned downstream of the inlet of the other streams that are to be heated by the heating streams. This is because the steam / hydrogen mixture flowing in the steam / hydrogen conduit 378 may require less heating than the other streams that are to be heated in order to exit the heat exchanger 310 at the desired temperature (e.g. 650°C-750°C), given the steam / hydrogen mixture flowing in the steam / hydrogen conduit 378 may enter the heat exchanger 310 at a higher temperature (e.g. 150°C-700°C) compared to the other streams that are to be heated. Introducing the steam / hydrogen mixture into the heat exchanger 310 in this way exposes the stream to less heat during passage through the heat exchanger 310 than the other streams that are to be heated. However, the steam / hydrogen inlet 317 may be located at a particular position along the heat exchanger 310 where, during operation, the temperature inside the heat exchanger 310 is approximately equal to the temperature of the steam / hydrogen mixture entering the heat exchanger 310 through the steam / hydrogen inlet 317. This may avoid the steam / hydrogen mixture entering a zone of the heat exchanger 310 that is cooler than the steam / hydrogen mixture, thereby avoiding unnecessary cooling of the steam / hydrogen mixture before it is again heated as it flows through the heat exchanger 310.

[0127] From the above, it will also be appreciated that the heat exchanger 310 of the electrolyser system 300 is similar to the heat exchangers 110, 210 of the fuel cell systems 100, 200 in that there are two heating streams flowing through the heat exchanger 310 that are configured to heat one or more other streams flowing through the heat exchanger 310.

[0128] In some embodiments, the heat exchanger 310 may not include the burner fuel flow path 314. In such embodiments, apart from any hydrogen gas being directed into the recirculation conduit 384 and / or hydrogen collection conduit 396, hydrogen gas flowing out of the hydrogen / steam heat exchanger 360 may flow directly to the fuel inlet 342 of the burner 340.

[0129] In some embodiments, the electrolyser system 300 may omit the recirculation conduit 384. In such embodiments, apart from any hydrogen gas being directed into the hydrogen collection conduit 396, hydrogen gas flowing out of the hydrogen / steam heat exchanger 360 will flow to the fuel inlet 342 of the burner 340 (e.g. directly or via the burner fuel flow path 314 of the heat exchanger 310).

[0130] In some embodiments, the electrolyser system 300 may omit the WHR heat exchanger 370. In such embodiments, the exhaust gas flowing out of the heat exchanger 310 may be released to atmosphere.

[0131] In some embodiments, the electrolyser system 300 may omit the hydrogen / steam heat exchanger 360. In such embodiments, a portion of hydrogen gas flowing out of the hydrogen gas flow path 315 of the heat exchanger 310 may flow directly to the fuel inlet 342 of the burner 340, a portion of hydrogen gas flowing out of the hydrogen gas flow path 315 of the heat exchanger 310 may be directed into the recirculation conduit 384 (if present), and / or a portion of hydrogen gas flowing out of the hydrogen gas flow path 315 of the heat exchanger 310 may be directed into the hydrogen collection conduit 396.

[0132] In some embodiments, the heat exchanger 310 may omit the water / steam flow path 316. In such embodiments, a source of steam may be coupled in fluid communication to the inlet 317 of the heat exchanger 310. The source of steam may be coupled in fluid communication to the inlet 317 of the heat exchanger 310 so as to draw hydrogen gas into the steam conduit 378 through the steam venturi 353 from the recirculation conduit 384 (ifpresent) as discussed above. Alternatively, the inlet 317 of the heat exchanger 310 may be coupled in fluid communication with a hydrogen / steam source. In such an embodiment, a hydrogen / steam mixture flowing from the hydrogen / steam source may draw hydrogen in the recirculation conduit 384 into the inlet 317 of the heat exchanger 310 similar to that describe above.

[0133] Although the electrolyser system 300 has been described as having a steam venturi 353, it will be appreciated that the steam venturi 353 may be replaced with a blower or any other suitable device capable of introducing hydrogen gas from the recirculation conduit 384 into the steam conduit 378.

[0134] Although the electrolyser system 300 has been described and illustrated as having a burner 340, it will be appreciated that the burner 340 may be replaced with any suitable alternate heating source (e.g. an electric heater). In such an embodiment, conduit 388 may be coupled in fluid communication with the inlet 321 of the heat exchanger 310 and conduit 391 may be omitted. Accordingly, in this embodiment, gases flowing into the inlet 321 of the heat exchanger 310 (via the electrolyser stack 330) would be sufficiently heated by the heating source so that they can provide heat to one or more of the other gases flowing through the heat exchanger 310 in a similar manner to that described above with respect to the exhaust gases flowing through the heat exchanger 310. In such an embodiment, such a heating source may be upstream (e.g. associated with conduit 387) or downstream (e.g. associated with conduit 388) of the electrolyser stack 330. Alternatively, the burner 340 may be replaced with two suitable alternate heating sources, one upstream (e.g. associated with conduit 387) of the electrolyser stack 330 and the other downstream (e.g. associated with conduit 388) of the electrolyser stack 330. Further, in this embodiment, no hydrogen gas would be directed to and through the burner fuel flow path 314 and then subsequently to the burner 340. Instead, hydrogen gas flowing in the hydrogen gas conduit 382 would be directed to the hydrogen collection conduit 396 and / or the recirculation conduit 384.

[0135] Figure 5 illustrates a reversible fuel cell / electrolyser system 400 according to another embodiment of the present disclosure. The system 400 includes a combination of features from fuel cell system 200 and electrolyser system 300. The system 400 istherefore similar to the fuel cell system 200 and the electrolyser system 300 apart from the inlet 417a, b of the heat exchanger 410 and the arrangement of features upstream of the inlet 417a,b of the heat exchanger 410.

[0136] Features of the system 400 that are identical or equivalent to those of the fuel cell system 200 are indicated with reference numerals that are equivalent to those of the fuel cell system 200 but incremented by 200. Features of the system 400 that are identical or equivalent to those of the electrolyser system 300 that are not found in the fuel cell system 200 are indicated with reference numerals that are equivalent to those of the electrolyser system 300 but incremented by 100. For features that are identical between the fuel cell system 200 and the electrolyser system 300, it will be appreciated that the above description of these features in relation to the fuel cell system 200 and the electrolyser system 300 is also applicable to the corresponding equivalent features of the system 400. Accordingly, the features that are common between the systems that have been described above in relation to the fuel cell system 200 and the electrolyser system 300 are not described again below in relation to the system 400.

[0137] The system 400 is capable of operating in two modes. In a first mode, the system 400 operates as a fuel cell system similar to that described above with respect to fuel cell system 200. In a second mode, the system 400 operates as an electrolyser system similar to that described above with respect to electrolyser system 300.

[0138] Differences between the system 400 and the fuel cell system 200 and the electrolyser system 300 are described below.

[0139] The system 400 includes both:• a hydrogen source 454 and a hydrogen venturi 453a, which are equivalent to the hydrogen source 254 and hydrogen venturi 253 of the fuel cell system 200, respectively; and• a steam conduit 478 and steam venturi 453b, which are equivalent to the steam conduit 378 and steam venturi 353 of the electrolyser system 300, respectively.

[0140] Given the system 400 includes both the hydrogen source 454 and the steam conduit 478, the steam / fuel flow path 411 of the heat exchanger 410 includes two inlets417a, and 417b. The inlet 417a is connected in fluid communication to the source of hydrogen 454 and the inlet 417b is connected in fluid communication with the steam conduit 478. Accordingly, both inlets 417a and 417b are in fluid communication with the steam / fuel flow path 411 of the heat exchanger 410.

[0141] Further, the recirculation conduit 484 of the system 400 is coupled in fluid communication with both the hydrogen venturi 453a and the steam venturi 453b.

[0142] In the first mode of operation, where the system 400 operates as a fuel cell system, the following features of the system 400 may be disabled or may not utilised:• the water / steam flow path 416 of the heat exchanger 410;• the steam conduit 478• the steam venturi 453b;• the hydrogen collection conduit 496; and• the inlet 417a of the heat exchanger 410.

[0143] The remaining features of the system 400 are enabled (i.e. utilised) in the first mode of operation. With the above combination of features disabled (or not utilised) and enabled, it will be appreciated that the system 400 in the first mode of operation is similar to the fuel cell system 200. Accordingly, in the first mode of operation, the system 400 may operate in a similar manner to that described above with respect to the fuel cell system 200. The above description of the fuel cell system 200 is therefore also applicable to the system 400 when operating the first mode of operation.

[0144] In certain implementations of the first mode of operation, one or more of the above-identified features may still be utilised if required to support specific operational conditions or transitional states. For example, features such as the steam conduit, venturi arrangements, and / or associated flow paths may be activated to assist in system balancing, thermal management, and / or pressure regulation, even though they are generally disabled in this mode. Where any of these features are utilised, they operate in the same manner as described above. The extent to which these features are employed may therefore vary depending on system configuration, control algorithms and real-time operatingrequirements.

[0145] In the second mode of operation, where the system 400 operates as an electrolyser system, the following features of the system 400 may be disabled or may not utilised:• the source of hydrogen 454;• the hydrogen venturi 453a;• the inlet 417b of the heat exchanger 410;• the cooling air conduit 489;• the cooling air bypass conduit 490;• the exhaust gas bypass conduit 493; and• the burner fuel bypass conduit 497.

[0146] The remaining features of the system 400 are enabled (i.e. utilised) in the second mode of operation. With the above combination of features disabled (or not utilised) and enabled, it will be appreciated that the system 400 in the second mode of operation is similar to the electrolyser system 300. Accordingly, in the second mode of operation, the system 400 may operate in a similar manner to that described above with respect to the electrolyser system 300. The above description of the electrolyser system 300 is therefore also applicable to the system 400 when operating the second mode of operation.

[0147] In certain implementations of the second mode of operation, one or more of the above-identified features may still be utilised if required to support specific operational conditions or system transitions. For example, components such as the cooling air pathways or bypass conduits may be utilised to maintain thermal stability or assist in system balancing, even though they are generally disabled in this mode. Where these features are utilised, they operate in the same manner as described above. The extent to which these features are used can therefore vary depending on system configuration, control strategies, and real-time operating requirements.

[0148] Features of the system 400 may be enabled and disabled using any suitable device / methods (e.g. one or more valves associated with the respective features).

[0149] Optional features described above with respect to the fuel cell system 200 and electrolyser system 300 may also be optional features for the system 400.

[0150] Although the system 400 has been described an illustrated as having both the hydrogen venturi 453a and the steam venturi 453b, it is envisaged that both the hydrogen venturi 453a and the steam venturi 453b may be replaced by a single venturi. In such an embodiment, both the steam conduit 478 and the source of hydrogen may be selectively (e.g. via a control valve or other suitable device) in fluid communication with the single venturi.

[0151] Further, the two inlets 417a and b of the heat exchanger 410 may be combined into a single inlet. In such an embodiment, both the steam conduit 478 and the source of hydrogen 454 may be coupled to the single inlet and selectively placed in fluid communication with the single inlet (e.g. via a control valve or other suitable device).

[0152] In an alternate embodiment of the system 400, the hydrogen venturi 453a and the inlet 417a of the heat exchanger 410 may be omitted. Accordingly, the source of hydrogen 454 would not be coupled in fluid communication with the inlet 417a of the heat exchanger 410 but may be selectively coupled in fluid communication with the steam venturi 453b (e.g. via a control valve). In this embodiment, when the system 400 is operated as a fuel cell system, the water / steam flow path 416 of the heat exchanger 410 would be enabled to generate steam and the source of hydrogen 454 would be placed in fluid communication with the steam venturi 453b. The generated steam would flow in and through the steam conduit 478. Steam flowing in the steam conduit 478 past the steam venturi 453b would draw hydrogen from the source of hydrogen 454 and hydrogen in the recirculation conduit 484 into the steam conduit 478 through the steam venturi 453b. Accordingly, when this embodiment is operated as a fuel cell system, a mixture of hydrogen and steam would flow into the flow path 411 of the heat exchanger 410 and the system 400 would operate in a similar manner to that described above with respect to systems 100 and 200. Further, in this embodiment, when the system 400 is operated as an electrolyser system, the source of hydrogen 454 may not be in fluid communication with the steam venturi 453b (e.g. via a control valve) and the system 400 would operate in a similar manner to the second mode of operation as described above.

[0153] Figure 6 illustrates a reversible fuel cell / electrolyser system 500 according to another embodiment of the present disclosure. The reversible fuel cell / electrolyser system500 is similar to the reversible fuel cell / electrolyser system 400. However, the reversible fuel cell / electrolyser system 500 does not include the source of hydrogen 454, the steam venturi 453b, the hydrogen venturi 453a, the inlet 417a, and the inlet 417b of the reversible fuel cell / electrolyser system 400. Instead, the reversible fuel cell / electrolyser system 500 includes a source of natural gas 554, a steam venturi 553, a steam conduit 595, a fuel conduit 578, a pre-reformer 550, and a steam bypass conduit 599. Accordingly, system 500 replaces the hydrogen-based feed architecture of system 400 with a natural-gas-based reforming architecture while retaining reversible fuel-cell / electrolyser functionality

[0154] Features of the system 500 that are identical or equivalent to those of the fuel cell system 400 are indicated with reference numerals that are equivalent to those of the fuel cell system 400 but incremented by 100. For features that are identical between the fuel cell system 400 and the electrolyser system 500, it will be appreciated that the above description of these features in relation to the fuel cell system 400 is also applicable to the corresponding equivalent features of the system 500. Accordingly, the features that are common between the systems that have been described above in relation to the fuel cell system 400 are not described again below in relation to the system 500.

[0155] The reversible fuel cell / electrolyser system 500 operates in a similar manner to that described above with respect to the reversible fuel cell / electrolyser system 400. Accordingly, the reversible fuel cell / electrolyser system 500 operates in two modes. In a first mode, the system 500 operates as a fuel cell system similar to that described above with respect to fuel cell system 100. In a second mode, the system 500 operates as an electrolyser system similar to that described above with respect to electrolyser system 300.

[0156] In the first mode of operation, where the system 500 operates as a fuel cell system, the following features of the system 500 may be disabled or may not be utilised:• the steam bypass conduit 599; and• the hydrogen collection conduit 596.

[0157] The remaining features of the system 500 are enabled (i.e. utilised) in the first mode of operation.

[0158] In the first mode of operation, the system 500 operates in a similar manner to the first mode of operation of the system 400. However, for the system 500, in the first mode of operation, steam flows through the steam conduit 595 into the inlet 551 of the prereformer 550. As steam flows past the steam venturi 553, natural gas from the source of natural gas 554 and burner fuel in the recirculation conduit 584 (if present) is drawn into the steam conduit 595 through the steam venturi 553 to be mixed with steam to create a steam / fuel mixture. The steam / fuel mixture flows into the pre-reformer 550 via the inlet 551. The steam / fuel mixture is partially reformed in the pre-reformer 550 (as described above with respect to pre-reformer 150). The pre-reformed steam / fuel mixture flows out of the pre-reformer 550 through the outlet 552, into and through the fuel conduit 578, and into the fuel inlet 517 of the fuel flow path 511 of the heat exchanger 510. The remainder of the first mode of operation of the system 500 is similar to that described above for the fuel cell system 100.

[0159] In the second mode of operation, where the system 500 operates as an electrolyser system, the following features of the system 500 may be disabled or may not be utilised:• the source of natural gas 554;• the steam venturi 553;• the cooling air conduit 589;• the cooling air bypass conduit 590;• the exhaust gas bypass conduit 593;• the recirculation conduit 584;• the burner fuel bypass conduit 597; and• the pre-reformer 550.

[0160] The remaining features of the system 500 are enabled (i.e. utilised) in the second mode of operation.

[0161] In the second mode of operation, the system 500 operates in a similar manner to the second mode of operation of the system 400. However, for the system 500, in the second mode of operation, the steam bypass conduit 599 is enabled and the source of natural gas 554, the steam venturi 553, and the pre-reformer 550 are disabled. Accordingly,in the second mode of operation, steam flowing in the steam conduit 595 flows into the steam bypass conduit 599, into the fuel conduit 578, and into the fuel inlet 517 of the fuel flow path 511 of the heat exchanger 510. Further, the recirculation conduit 584 may be placed in fluid communication with the steam bypass conduit 599 such that steam flowing in the steam bypass conduit 599 draws hydrogen in the recirculation conduit 584 into the steam bypass conduit 599. This produces a hydrogen / steam mixture that flows through the fuel conduit 578 and into the fuel inlet 517 of the fuel flow path 511 of the heat exchanger 510. The recirculation conduit 584 may be placed in fluid communication with the steam bypass conduit 599 via an additional steam venturi (not shown) associated with the steam bypass conduit 599, so that steam flowing in the steam bypass conduit 599 draws hydrogen in the recirculation conduit 584 into the steam bypass conduit 599 through this additional steam venturi. The recirculation conduit 584 may be selectively placed in fluid communication with the steam venturi 553 when operating in the first mode of operation, and with the steam bypass conduit 599 when operating in the second mode of operation, for example via one or more valves (or any other suitable device). The remainder of the second mode of operation of the system 500 is similar to that described above for the electrolyser system 300.

[0162] Features of the system 500 may be enabled and disabled using any suitable device / methods (e.g. one or more valves associated with the respective features).

[0163] Optional features described above with respect to the fuel cell system 100 and electrolyser system 300 may also be optional features for the system 500.

[0164] In an alternate embodiment, the system 500 may omit the steam bypass conduit 599. In this embodiment, in the first mode of operation, the system 500 would operate as described above. However, in the second mode of operation, steam flowing past the steam venturi 553 in the steam conduit draws hydrogen in the recirculation conduit 584 into the steam conduit 595 through the steam venturi 553, which creates a steam / hydrogen mixture. The steam / hydrogen mixture flows into and through the pre-reformer 550, through the fuel conduit 578, and into the fuel inlet 517 of the fuel flow path 511 of the heat exchanger 510. The remainder of the second mode of operation of the system 500 is similar to that described above for the electrolyser system 300.

[0165] Although the heat exchangers 110, 210, 310, 410, 510 have been described above as exchanging heat via a predominantly counterflow arrangement, where the heating streams flow in the opposite direction through the heat exchangers 110, 210, 310, 410, 510 compared to the streams that are to be heated, it is envisaged that the heat exchangers 110, 210, 310, 410, 510 may use other flow arrangements for exchanging heat between the heating streams and the streams to be heated. For example, the heat exchangers 110, 210, 310, 410, 510 may use a crossflow arrangement where the heating streams flow at an angle to the streams to be heated through the heat exchangers 110, 210, 310, 410, 510 or a parallel flow where the heating streams flow in a common direction with the streams to be heated through the heat exchangers 110, 210, 310, 410, 510. Further, it is envisaged that the heat exchangers 110, 210, 310, 410, 510 may use any combination of counterflow, crossflow, and parallel flow arrangements to exchange heat between the heating streams and the streams to be heated in the heat exchangers 110, 210, 310, 410, 510.

[0166] It will be appreciated from the above that the stacks 130, 230, 330, 430 are electrochemical devices having one or more electrochemical cells. Accordingly, the heat exchanger disclosed herein may be used in electrochemical systems comprising an electrochemical device composed of one or more electrochemical cells.

[0167] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.

[0168] By way of clarification and for avoidance of doubt, as used herein and except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additions, components, integers or steps

[0169] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

47CLAIMS1. A heat exchanger for a fuel cell or electrolyser system, the heat exchanger comprising:a first heated fluid flow path configured to direct a first fluid through the heat exchanger, an outlet of the first heated fluid flow path configured to be coupled in fluid communication with a first inlet of a fuel cell or electrolyser stack of the fuel cell or electrolyser system;a second heated fluid flow path configured to direct air through the heat exchanger, an inlet of the second heated fluid flow path configured to be in fluid communication with a source of air, and an outlet of the second heated fluid flow path configured to be coupled in fluid communication with a second inlet of the fuel cell or electrolyser stack;a first heating fluid flow path configured to direct a first heating fluid from a heating source of the fuel cell or electrolyser system through the heat exchanger, an inlet of the first heating fluid flow path configured to receive the first heating fluid from the heating source;a second heating fluid flow path configured to direct a second heating fluid from the fuel cell or electrolyser stack through the heat exchanger, an inlet of the second heating fluid flow path configured to be coupled in fluid communication with a first outlet of the fuel cell or electrolyser stack,wherein:the first fluid flowing through the first heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path; andair flowing through the second heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path.

2. The heat exchanger of claim 1, wherein an outlet of the second heating fluid flow path is configured to be coupled in fluid communication with a second heat exchanger such that the second heating fluid flowing out of the second heating fluid flow path flows into and through the second heat exchanger.

483. The heat exchanger of claim 2, further comprising a third heated fluid flow path configured to direct a combustible gas through the heat exchanger, wherein:an inlet of the third heated fluid flow path is configured to be coupled in fluid communication with an outlet of the second heat exchanger such that combustible gas flowing out of the outlet of the second heat exchanger flows into and through the third heated fluid flow path of the heat exchanger; andthe combustible gas flowing through the third heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path.

4. The heat exchanger of claim 3, wherein:the heating source is a burner;an outlet of the third heated fluid flow path is configured to be coupled in fluid communication with a burner fuel inlet of the burner such that combustible gas flowing out of the third heated fluid flow path flows into the burner; andthe first heating fluid is exhaust gas produced by the burner combusting the combustible gas.

5. The heat exchanger of any one of the preceding claims, wherein an outlet of the first heating fluid flow path is configured to be coupled in fluid communication with a third heat exchanger such that the first heating fluid flowing out the first heating fluid flow path flows into and through the third heat exchanger.

6. The heat exchanger of any one of the preceding claims, wherein the first fluid is hydrogen from a source of hydrogen and the inlet of the first heated fluid flow path is in fluid communication with the source of hydrogen.

7. The heat exchanger of any one of claims 1-5, further comprising a fourth heated fluid flow path configured to direct water / steam through the heat exchanger, an inlet of the fourth heated fluid flow path configured to be in fluid communication with a source of water, wherein water flowing through the fourth heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or the second heating fluid flowing through the second heating fluid flow path.

498. The heat exchanger of claim 7, wherein:a steam outlet of the fourth heated fluid flow path is configured to be in fluid communication with the inlet of the first heated fluid flow path; andsteam flowing from the steam outlet of the fourth heated fluid flow path to the inlet of the first heated fluid flow path is configured to draw fuel from a source of fuel into the first heated fluid flow path.

9. The heat exchanger of claim 8, wherein the first fluid comprises a mixture of steam and hydrogen.

10. The heat exchanger of claim 8 or 9, wherein the source of fuel is natural gas, liquid petroleum gas, ethane, propane, butane, pentane, or methanol.

11. A fuel cell or electrolyser system comprising:a fuel cell or electrolyser stack;a heating source;a heat exchanger having:a first heated fluid flow path to direct a first fluid through the heat exchanger, an outlet of the first heated fluid fuel flow path coupled in fluid communication with a first inlet of the fuel cell or electrolyser stack;a second heated fluid flow path to direct air through the heat exchanger, an inlet of the second heated fluid flow path is in fluid communication with a source of air, and an outlet of the second heated fluid flow path coupled in fluid communication with a second inlet of the fuel cell or electrolyser stack;a first heating fluid flow path to direct a first heating fluid from the heating source through the heat exchanger, an inlet of the first heating fluid flow path configured to receive the first heating fluid from the heating source; anda second heating fluid flow path to direct a second heating fluid from the fuel cell or electrolyser stack through the heat exchanger, an inlet of the second heating fluid flow path coupled in fluid communication with a first outlet of the fuel cell or electrolyser stack,wherein:50the first fluid flowing through the first heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path; andair flowing through the second heated fluid flow path is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path.

12. The system of claim 11, further comprising a second heat exchanger having a first flow path and a second flow path, wherein:an outlet of the first heating fluid flow path of the heat exchanger is coupled in fluid communication with an inlet of the first flow path of the second heat exchanger such that the first heating fluid flowing out of the first heating fluid flow path of the heat exchanger flows into and through the first flow path of the second heat exchanger; andthe first heating fluid flowing through the first flow path of the second heat exchanger is configured to heat water flowing through the second flow path of the second heat exchanger.

13. The system of claim 12, further comprising a bypass conduit coupling an outlet of the heating source in fluid communication with the inlet of the first flow path of the second heat exchanger and bypassing the first heating fluid flow path of the heat exchanger, wherein the bypass conduit is configured to vary a flow rate of the first heating fluid flowing into the bypass conduit and bypassing the first heating fluid flow path of the heat exchanger.

14. The system of any one of claims 11-13, further comprising a third heat exchanger having a first flow path and a second flow path, wherein:an outlet of the second heating fluid flow path of the heat exchanger is coupled in fluid communication with an inlet of the first flow path of the third heat exchanger such that the second heating fluid flowing out of the second heating fluid flow path of the heat exchanger flows into and through the first fluid flow path of the third heat exchanger; andwater flowing through the second flow path of the third heat exchanger is configured to cool the second heating fluid flowing through the first flow path of the third heat exchanger and condense water vapour in the second heating fluid.

15. The system of claim 14, wherein:the second heating fluid flowing out of an outlet of the first flow path of the third heat exchanger comprises a combustible gas;the heat exchanger further comprises a third heated fluid flow path to direct the combustible gas through the heat exchanger;an inlet of the third heated fluid flow path is coupled in fluid communication with the outlet of the first flow path of the third heat exchanger such that the combustible gas flowing out of the first flow path of the third heat exchanger flows into and through the third heated fluid flow path of the heat exchanger; andthe combustible gas flowing through the third heated fluid flow path of the heat exchanger is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path.

16. The system of claim 15, wherein:the heating source is a burner having:an exhaust outlet coupled in fluid communication with the inlet of the first heating fluid flow path of the heat exchanger; anda burner fuel inlet coupled in fluid communication with an outlet of the third heated fluid flow path of the heat exchanger such that the combustible gas flowing out of the third heated fluid path flows into the burner fuel inlet; andthe first heating fluid is exhaust gas produced by the burner combusting the combustible gas.

17. The system of claim 15 or 16, further comprising a recirculation conduit in fluid communication with the inlet of the first heated fluid flow path of the heat exchanger and the outlet of the first flow path of the third heat exchanger, wherein the recirculation conduit is configured to vary a flow rate of the combustible gas from the third heatexchanger flowing into the recirculation conduit to the inlet of the first heated fluid flow path of the heat exchanger.

18. The system of claim 17, wherein the inlet of the first heated fluid flow path is in fluid communication with a source of fuel, the system further comprising:a venturi in fluid communication with the recirculation conduit and the source of fuel, wherein fuel flowing from the source of fuel to the inlet of the first heated fluid flow path of the heat exchanger is configured to draw combustible gas in the recirculation conduit into the inlet of the first heated fluid flow path of the heat exchanger through the venturi.

19. The system of any one of claims 11-18, wherein the first fluid comprises hydrogen.

20. The system of any one of claims 11-16, wherein:the heat exchanger further comprises a fourth heated fluid flow path to direct water / steam through the heat exchanger, an inlet of the fourth heated fluid flow path in fluid communication with a source of water; andwater flowing through the fourth heated fluid flow path of the heat exchanger is configured to be heated by the first heating fluid flowing through the first heating fluid flow path and / or by the second heating fluid flowing through the second heating fluid flow path.

21. The system of claim 20, wherein:a steam outlet of the fourth heated fluid flow path is in fluid communication with the inlet of the first heated fluid flow path; andsteam flowing from the steam outlet to the inlet of the first heated fluid flow path is configured to draw fuel from a source of fuel into the first heated fluid path.

22. The system of claim 20, further comprising a pre-reformer disposed between, and coupling in fluid communication, a source of fuel and the inlet of the first heated fluid flow path, wherein:the pre-reformer is configured to at least partially reform fuel from the source of fuel;53a steam outlet of the fourth heated fluid flow path is in fluid communication with an inlet of the pre-reformer; andsteam flowing from the steam outlet to the inlet of the pre-reformer is configured to draw fuel from the source of fuel into the pre-reformer.

23. The fuel cell system of 22, when dependent on any one of claims 14-16, further comprising a recirculation conduit in fluid communication with the inlet of the prereformer and the outlet of the first flow path of the third heat exchanger, wherein the recirculation conduit is configured to vary a flow rate of the combustible gas from the third heat exchanger flowing into and through the recirculation conduit to the inlet of the prereformer.

24. The fuel cell system of claim 23, further comprising a venturi in fluid communication with the source of fuel, the inlet of the pre-reformer, and the recirculation conduit, wherein steam flowing from the steam outlet to the inlet of the pre-reformer is configured to draw fuel from the source of fuel and combustible gas in the recirculation conduit through the venturi and into the inlet of the pre-reformer.

25. The fuel cell system of any one of claims 21-24, wherein the source of fuel is a source of natural gas, liquid petroleum gas, ethane, propane, butane, pentane, or methanol.

26. The fuel cell system of any one of claims 16-25, wherein an air outlet of the fuel cell or electrolyser stack is coupled in fluid communication to an air inlet of the burner, wherein the air inlet of the burner is configured to provide air for combusting fuel in the burner.

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