Integrated fuel cell and heat engine hybrid system for high efficiency power generation

A fuel cell and heat engine hybrid system using a high-temperature fuel cell having an anode compartment adapted to receive fuel from a fuel supply path and to output anode exhaust gas and a cathode compartment adapted to receive oxidant gas and to output cathode exhaust gas. A heat engine assembly is adapted to receive oxidant gas and a further gas comprising one of the anode exhaust gas and a gas derived from the anode exhaust gas and to cause oxidation of the further gas and generate output power, the heat engine also generating heat engine exhaust including oxidant gas. The heat engine exhaust is then used to provide oxidant gas to the cathode compartment of the fuel cell.

BACKGROUND OF THE INVENTION

This invention relates to fuel cell production systems and, in particular, to a fuel cell system integrated with a heat engine such as an internal combustion engine and an external combustion engine.

A fuel cell is a device, which directly converts chemical energy stored in hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode electrode and a cathode electrode separated by an electrolyte, which serves to conduct electrically charged ions.

A fuel cell may be combined with a heat engine such as a turbine generator to produce a high efficiency system, commonly called a hybrid system. In a commonly practiced hybrid system, a fuel cell typically is situated in the position normally occupied by the combustor of the turbine generator so that air compressed by the turbine generator compressor section is heated and then sent to the fuel cell cathode section. In this arrangement, the fuel cell is operated at a high pressure, which substantially increases the cost of the power plant hardware. The high pressure operation of the fuel cell inhibits the use of internal reforming in the fuel cell which further increases the plant cost and reduces efficiency, and subjects the fuel cell to potentially damaging pressure differentials in the event of plant upset. Furthermore, the fuel cell pressure is coupled with the gas turbine pressure, reducing the reliability of operation and limiting the application to system designs where the gas turbine pressure is nearly matched with the fuel cell pressure.

To overcome these disadvantages, another hybrid system has been developed where a heat engine in the form of a turbine generator is bottomed with a fuel cell so that the heated air discharged from the gas turbine is delivered to the cathode section of the fuel cell. U.S. Pat. No. 6,365,290, assigned to the same assignee hereof, discloses such a hybrid fuel cell/gas turbine system, in which waste heat from the fuel cell is used by a heat recovery unit to operate the heat engine cycle, and the system is arranged such that the compressed oxidant gas, heated in the heat recovery unit and by a high temperature heat exchanger, is expanded in the expansion cycle of the heat engine. It is then passed through an oxidizer (also commonly called combustor or burner), which also receives the anode exhaust, passed through the heat exchanger and the resultant gas delivered to the cathode section of the fuel cell.

In a modification of the system of the '290 patent, U.S. Pat. No. 6,896,988 assigned to the same assignee hereof, discloses an enhanced hybrid system for high temperature fuel cells including solid oxide and molten carbonate fuel cells which expands the applicability of the system of the '290 patent by providing a better match between the fuel cell size and the gas turbine. Despite the benefits provided by the system of the '988 patent, there are limitations to its application.

Both the systems of the '290 and '988 patents are intended for generation of electricity at very high efficiencies. However, they require a relatively high temperature heat exchanger, which may be very costly especially for large-scale power plants (>10 MW). Also, the aforesaid systems need to be more flexible if they are to be used in system configurations which are needed to better satisfy compromises between efficiency and power generation.

It therefore would be desirable to provide an alternative fuel cell and heat engine hybrid system having high efficiencies and providing greater flexibility in balancing power between a high temperature fuel cell such as a solid oxide or molten carbonate fuel cell and a heat engine assembly such as a compressor/turbine assembly.

It would also be desirable to provide a fuel cell and heat engine hybrid system which is better able to mitigate against the need for a high temperature heat exchanger (recuperator or regenerator) to be operated above the fuel cell cathode exhaust temperature.

It would further be desirable to provide a hybrid fuel cell and heat engine hybrid system, which may offer a less expensive alternative system configuration to the ones described in '290 and '988 patents for high temperature and near atmospheric pressure fuel cells.

SUMMARY OF THE INVENTION

A fuel cell and heat engine hybrid system comprising a high temperature fuel cell and a heat engine assembly is disclosed. The system is adapted so that oxidant gas such as air and a further gas comprising anode exhaust gas or gas derived from the anode exhaust gas of the fuel cell serve as inputs to the heat engine assembly. Oxidation (also referred to as burning or combustion) of the further gas occurs in the heat engine assembly and the heat engine assembly generates power and outputs a heat engine exhaust gas which includes oxidant gas. The heat engine exhaust gas is then used to provide oxidant gas to the cathode of the fuel cell. In certain cases, the anode exhaust is processed to remove some or all of the water content in the exhaust and/or compressed or pressurized to produce the further gas.

The heat engine assembly can include any variety of an Internal Combustion Engine such as a combustion turbine, a 4-cycle spark ignited (SI) reciprocating engine, and a 2-cycle compression ignited (CI) engine. The heat engine can also include an externally heated or fired heat engine such as Sterling engine, a turbocharger or a gas turbine.

A number of fuel cell and heat engine hybrid system configurations based on the type of fuel, such as natural gas, liquid fuel, etc, can be configured. Additionally, numerous components and heat exchanging arrangements can also be implemented with the different integrated fuel cell and heat engine system configurations.

The fuel cell and heat engine hybrid system disclosed hereinafter comprises a fuel cell having an anode section and a cathode section, a heat engine assembly comprising a gas turbine having a compressor section or cycle compressing oxidant supply gas and an expansion section or cycle, and a heat recovery unit responsive to exhaust gas from the cathode section of the fuel cell. The heat recovery unit heats and humidifies a fuel supply gas such as natural gas or syngas supplied by a gasifier before the fuel supply gas is fed to the anode compartment of the fuel cell.

In the disclosed system, the anode exhaust gas, optionally, is cooled and the product water is removed by a condenser. The cooled anode exhaust gas containing residual fuel not utilized in the fuel cell is then optionally compressed in a gas compressor and thereafter flows to a combustor or oxidizer forming a part of the heat engine assembly and which also receives heated compressed oxidant gas. The gas compressor boosting of the pressure of the anode exhaust gas helps bring the pressure of the gas output of the oxidizer up to the inlet pressure of the expansion cycle or section of the gas turbine of the heat engine assembly. The anode exhaust gas is then oxidized in the oxidizer and the output of the oxidizer including heated compressed oxidant gas is supplied to the expansion cycle or section of the gas turbine of the heat engine assembly. This results in a mechanical power output from the expansion section and an exhaust gas comprising oxidant gas which is then used as the oxidant gas for the cathode section of the fuel cell.

Also, in the disclosed system, the oxidant supply gas is compressed or pressurized in the compressor section or cycle of the heat engine assembly and is optionally heated in the heat recovery unit by the cathode exhaust gas to which, as above-mentioned, the heat recovery unit is responsive. This compressed heated oxidant supply gas then flows to the oxidizer or combustor of the heat engine assembly, as also above-mentioned. With the hybrid system, therefore, the recovery of waste heat from the fuel cell combined with the oxidation of the anode exhaust gas in the heat engine assembly results in very high system efficiencies.

In certain cases, supplemental air from a blower is combined with the exhaust gas from the expansion section of the gas turbine before it is fed to the cathode section of the fuel cell. The combined gas ensures a required cathode flow for both the oxidant gas and the removal of waste heat from the fuel cell.

DETAILED DESCRIPTION

FIG. 1shows a block diagram of a hybrid fuel cell and heat engine system1for supplying power to a load. The system1comprises a high-temperature fuel cell2and a heat engine assembly30. The fuel cell2includes an anode compartment3and a cathode compartment4separated by an electrolyte matrix. The anode compartment3is adapted to receive fuel from a fuel supply path6and to output anode exhaust. The cathode compartment4is adapted to receive oxidant gas and to output cathode exhaust. The hybrid system also optionally includes a water transfer assembly9for transferring water in the anode exhaust to the fuel supply path6and for outputting water-separated anode exhaust.

The fuel cell2can be any type of high temperature fuel cell such as a molten carbonate fuel cell or solid oxide fuel cell.

The heat engine assembly30can include any variety of the Internal Combustion Engine such as a combustion turbine, a 4-cycle spark ignited (SI) reciprocating engine, and a 2-cycle compression ignited (CI) engine. The heat engine assembly30can also include an externally heated or fired heat engine such as Sterling engine, a turbocharger or a gas turbine. In the illustrative case shown, the heat engine assembly30comprises a compressor/turbine having a compression cycle or section16and a turbine or expansion section or cycle21. The heat engine assembly also includes an oxidizer (also called a combustor or burner)18.

Oxidant supply gas, shown as air, is compressed or pressurized in the compression section or cycle16of the heat engine assembly30. The compressed oxidant gas is then fed to a heat recovery unit15also included in the hybrid system1. In particular, the compressed oxidant gas is received in a heat exchanger section17of the heat recovery unit15and is heated by cathode exhaust gas delivered to the unit15from the cathode compartment4of the fuel cell2. The oxidizer18, forming a part of the heat engine assembly30, is adapted to receive the compressed heated oxidant gas (air) from the heat exchanger17. The oxidizer18also receives a further gas which comprises or is derived from the anode exhaust gas from the anode compartment3of the fuel cell2.

In the illustrative case shown, the anode exhaust gas is passed through the water transfer assembly9which condenses and transfers water from the exhaust. The water-separated anode exhaust passed form the water transfer assembly9is then pressurized in an anode exhaust compressor32, and the pressurized water-separated anode exhaust gas forms the above-mentioned further gas fed to the oxidizer18.

The oxidizer18inFIG. 1is configured as a combustor external to the compressor/turbine of the heat engine assembly30. The oxidizer18can also be configured as an internal combustor as practiced, for example, in an ICE (Internal Combustion Engine), a 4-cycle spark ignited reciprocating engine, and a 2-cycle compression ignited engine. Moreover, the oxidizer18can either be a catalytic oxidizer or fired burner as practiced in combustion turbines.

In the oxidizer18, the pressurized water-separated anode exhaust is oxidized with the heated compressed oxidant gas to result in an output gas which comprises compressed heated oxidant gas. The oxidizer output gas is then fed to the expansion section or turbine21of the heat engine assembly30where expansion of the gas results in mechanical power generation. The exhaust gas from the expansion section comprising expanded oxidant gas is then used to provide oxidant gas to the cathode compartment4of the fuel cell2.

It should be noted that in the case of a 4-cycle SI or a 2-cycle CI used as the heat engine assembly30, the low pressure water-separated anode exhaust does not need to be compressed before being fed to the heat engine assembly. In such situations, the anode exhaust compressor32need not be used in the system1. Also, in certain cases, for example, at a very high gas turbine pressure ratio, the compressed air in the oxidant supply path5may not need to be heated by a heat exchanger. The system1will now be described in more detail below.

As shown inFIG. 1, a hydrocarbon containing fuel is supplied from a fuel supply (not shown for purposes of clarity and simplicity) to a fuel supply path6which carries the fuel to an inlet3A of the anode compartment3of the fuel cell2. In particular, as shown, the supply line6carries the fuel through a desulfurizer6A, which removes sulfur-containing compounds present in the fuel. The desulfurizer6A comprises one or more sulfur-adsorbent or sulfur-absorbent beds through which the fuel flows and which adsorb or absorb any sulfur-containing compounds in the fuel.

After being passed through the desulfurizer6A, the fuel in the supply line6is combined with water from the water transfer assembly9via a water supply line13to produce humidified fuel. The humidified fuel is then pre-heated in the heat recovery unit15via a further heat exchanger6B included in the unit15and also subjected to the cathode exhaust gas supplied to the unit. The pre-heated humidified fuel is then passed through a deoxidizer/preconverter unit6D, which removes any, trace oxygen and heavy hydrocarbon contaminants from the fuel. Although not shown inFIG. 1, another heat exchanger may be utilized after the deoxidizer/preconverter unit6D to raise the temperature of the fuel stream to a higher level as required by the anode3of the fuel cell assembly2. The pre-heated deoxidized humidified fuel is then supplied to the anode compartment3through the inlet3A.

Fuel entering the anode compartment3through the anode inlet3A may be reformed internally to produce hydrogen and carbon monoxide and undergoes an electrochemical reaction with oxidant gas passing through the cathode compartment4of the fuel cell2. Anode exhaust gas produced in the anode compartment3exits the fuel cell2through the anode outlet3B into an anode exhaust path7. The anode exhaust gas in the exhaust path7comprises a mixture of unreacted hydrogen, carbon monoxide, water vapor, carbon dioxide and trace amounts of other gases.

As shown inFIG. 1, the anode exhaust in the exhaust path7is passed to the water transfer assembly9which includes a condensing heat exchanger6C, also called a condenser, a knock out pot11and a pump14. The anode exhaust gas is cooled in the condensing heat exchanger6C so that water present in the anode exhaust condenses and a mixture of liquid water and an exhaust gas comprising the remaining components of the anode exhaust gas is formed. The mixture of the exhaust gas and water steam is thereafter passed through the knock out pot11in which water is separated from the exhaust gas and water-separated anode exhaust is outputted to the anode exhaust path7. Water that is separated in the knock out pot11is passed through the pump14which increases the pressure of the water. Separated and pressurized water is thereafter carried to the fuel supply path6via the water supply line13. In addition, any excess water produced in the knock out pot11and the pump14may be exported from the system1through a connecting line12.

In this illustrative case, a common knock out pot and pump are suitable for use in the system1for separating and increasing the pressure of the water. As can be appreciated, other water transfer devices or assemblies, such as a partial-pressure swing water transfer device, a conventional enthalpy wheel humidifier, a cooling radiator, a membrane, a packed column or an absorber/stripper type system may be used in place of, or with the heat exchanger6C, knock out pot11and the pump14for transferring part or all of the water.

The water-separated anode exhaust exits the knock out pot11and comprises primarily hydrogen and CO (carbon monoxide) fuel and CO2with trace amounts of water and unconverted hydrocarbons (typically methane). This water-separated anode exhaust gas is carried by the anode exhaust path7from the knock out pot11to the anode exhaust compressor32, and then, after being compressed, to the oxidizer18where it is mixed with heated and compressed oxidant gas or air in the line5from heat exchanger17. The compressed water-separated anode exhaust gas in the path7is oxidized by the heated compressed oxidant gas in the oxidizer18so as to produce an output gas comprising heated compressed oxidant gas at a higher temperature.

The output gas from the oxidizer18is carried by the line22to the expansion section or turbine21of the heat engine assembly30where it is expanded. The expansion process produces mechanical power which is converted by a generator31to electric power. In place of the generator31, a high speed alternator may be utilized to convert the mechanical power derived from the turbine21into the electric power.

In the illustrative case shown inFIG. 1, the fuel cell direct current (dc) electrical output is converted to an alternating current (ac) electrical output in a dc-to-ac inverter32. The electric output from generator31and the dc-to-ac inverter32are combined at33and the combined power directed to a utility grid or a customer's load.

In certain cases, the oxidizer18is also supplied with supplemental fuel from a supplemental fuel supply (not shown) via a supplemental fuel supply path26. In the oxidizer18, unspent fuel including hydrogen, CO, and hydrocarbons in the water-separated anode exhaust and any supplemental fuel provided are burned in the presence of the heated compressed oxidant gas, i.e., air, from the heat recovery unit15. The resultant hot compressed oxidant gas is thus suitable for production of mechanical power in the expansion section21of the heat engine assembly30.

In certain cases, a supplemental air path, shown as path35inFIG. 1, may be utilized to provide additional air in excess of the oxidant provided by the heat engine. One of the reasons for using the supplemental air in path35is to control temperatures at the cathode inlet4A and the cathode outlet4B. The supplemental air path35is provided by air blower36and is combined with the heat engine exhaust in the exhaust path24before entering the fuel cell.

Also, the exhaust from the expansion section, comprising primarily expanded oxidant gas, i.e., O2, N2and CO2, is led by the cathode oxidant gas path24, combined with the supplemental air in the path35, and directed to an inlet4A of the cathode compartment4where it undergoes electrochemical reaction. Cathode exhaust gas, as discussed above, exits the cathode compartment4through a cathode outlet4B and is carried by a cathode exhaust path28to and through the heat exchanger17, in which the cathode exhaust is cooled, thereby heating up the pressurized oxidant supply gas or air in the path5. The cathode exhaust gas in the exhaust path28is then cooled further in passing through the heat exchanger6B, thereby heating up and humidifying the fuel in the path6. The cooled cathode exhaust gas is then eliminated from the system1and/or used in further waste heat recovery. Thus, the heat energy stored in the cathode exhaust gas leaving the system1may be used in other applications, such as residential heating.

Table 1 shows a comparison of a nominal 300 kW system based on the system ofFIG. 1using a carbonate fuel cell versus a nominal 300 kW system based on the system of the above-mentioned '290 patent. As can be appreciated, the system ofFIG. 1has a comparable power and slightly better efficiency than the system of '290 patent. The high anode exhaust compression power is more than compensated by the higher gas turbine power in the system ofFIG. 1as compared to the system of the '290 patent. The 300 kW system based on the system ofFIG. 1has a higher turbine inlet temperature (shown as path22inFIG. 1) and gas turbine power as compared to the turbine inlet temperature and gas turbine power of the system based on the '290 patent which is limited by the materials used in a high temperature recuperator.

As discussed above, the system inFIG. 1utilizes a particular heat exchanging and system component arrangement and, in particular, a heat engine assembly30comprising a compressor/turbine. In other illustrative cases, the system can employ other heat engine assemblies, such as a combustion turbine, a recuperative turbine, or a microturbine. In such cases, the components of the system and heat exchangers employed, and the arrangement thereof, may vary, and additional components may be used, so as to achieve optimum efficiency. An illustration of a further arrangement hybrid system is shown inFIG. 2. However, it is noted that while the system arrangements ofFIGS. 1 and 2demonstrate the present hybrid system, it is evident to those of skill in the art that the system can be can be implemented in numerous other system configurations and heat exchanging arrangements.

FIG. 2shows an alternate arrangement of fuel cell and heat engine hybrid system300. The system300includes a heat engine assembly330which comprises a gas turbine having compression and expansion sections330A and330B and which further comprises an oxidizer325. The system300also includes a high temperature fuel cell302integrated with the heat engine assembly330. The operation of the system300and the supply and flow of fuel and other operating materials to the fuel cell302and the heat engine assembly330are controlled using a control assembly, as discussed in more detail below.

As shown inFIG. 2, the high-temperature fuel cell302comprises an anode compartment303and a cathode compartment304separated by an electrolyte matrix305. The anode compartment303of the fuel cell302is supplied with fuel from a fuel supply (not shown) carried by a fuel supply path306. As shown, fuel carried in the fuel supply path306is desulfurized in a desulfurizer306A and then combined with water and pre-heated in a humidifying heat exchanger306C.

In particular, the heat exchanger306C receives recycled water from a water supply path313, as discussed in more detail herein below, and the pre-heating of the fuel and water mixture is accomplished by passing cathode exhaust gas through the heat exchanger306C to recover heat energy stored in the cathode exhaust. The humidified fuel is passed through another heat exchanger306B, in which the fuel is further pre-heated by recovering heat from anode exhaust gas and thereafter deoxidized in a deoxidizer/pre-reformer306D, which removes any trace oxygen and heavy hydrocarbon contaminants from the fuel. Deoxidized and pre-reformed fuel is then supplied to the anode303through an anode inlet303A.

In the anode compartment, fuel undergoes an electrochemical reaction and spent fuel leaves the anode compartment303through an anode outlet303B as anode exhaust gas. Anode exhaust gas is carried by an anode exhaust path307from the anode outlet303B, and is passed through heat exchangers307A and306B to cool the anode exhaust before carrying the exhaust to a water transfer assembly309. In this illustrative case shown, the water transfer assembly309includes a cooling radiator or air-cooled heat exchanger309A which condenses out and separates the water from the anode exhaust gas, and a pump309B, which increases the pressure of the water separated by the cooling radiator or air-cooled heat exchanger309A. Water separated by the transfer assembly309is then carried out by the water supply path313and provided to the humidifying heat exchanger306C. The cooling radiator or air-cooled heat exchanger309A also outputs water-separated anode exhaust comprising remaining components of the anode exhaust, i.e. hydrogen, CO2and trace amounts of water and CO.

It is understood that the configuration of the water transfer assembly309is not limited to the arrangement shown inFIG. 2. For example, the water transfer assembly shownFIG. 1or any other suitable water transfer device or assembly may be used in place of the water transfer assembly309shown inFIG. 2. Moreover, excess water may be exported out of the system300via a water exhaust path339.

The water-separated anode exhaust gas is carried out of the water transfer assembly309by the anode exhaust path307. In certain cases, supplemental fuel from a supplemental fuel supply, for example a slip stream of the desulfurized fuel from the desulfurizer306A, is added to the water-separated anode exhaust gas via a supplemental fuel supply path322. In certain cases, the source of the supplemental fuel may also be different than the main fuel supply. The amount of supplemental fuel added to the water-separated anode exhaust gas is controlled based on the detected power demand, such that no supplemental fuel is added during low power demands exceeded by the power produced by the fuel cell302and a pre-selected amount of supplemental fuel is controlled to be added to the water-separated anode exhaust during higher power demands.

The water-separated anode exhaust, or the mixture of water-separated anode exhaust and supplemental fuel, is carried to an anode boost compressor327. The compressor327compresses these gases, and thereafter passes them to the heat exchanger307A in which the compressed water-separated anode exhaust, or the mixture of water-separated anode exhaust and supplemental fuel, is heated by the hot exhaust gas from the anode303.

The compressed heated water-separated anode exhaust gas, or the compressed heated mixture of water-separated anode exhaust and supplemental fuel, is then carried to an oxidizer325of the heat engine330, which also receives compressed pre-heated oxidant gas in the form of air from a supply path321. In particular, air is supplied from the path321to the compressor section330A of the gas turbine of the heat engine330, in which the air is compressed, and the compressed air is further heated in a heat exchanger328A by the cathode exhaust. Further heating of the compressed air may be done by a start-up heater321A, but normally the heater is used only when starting the turbine in a configuration where supplemental fuel is unavailable.

The compressed heated air is then combined with the water-separated anode exhaust, or the mixture of water-separated anode exhaust and supplemental fuel, in the oxidizer325, which oxidizes the resulting mixture to produce an output gas comprising hot compressed oxidant gas. A turbine section330B of the gas turbine of the heat engine330then allows expansion of the hot compressed gas from the oxidizer and outputs mechanical power and also outputs turbine exhaust gas comprising primarily CO2, O2and N2. In cases where the fuel cell is operated at high fuel utilization and no supplemental fuel is used to maximize efficiency, the water-separated anode exhaust gas may be very low in heat content and require the oxidizer325to include a catalyst to promote the complete combustion of the water-separated anode exhaust gas.

In certain cases, a supplemental air path, shown as path341(dotted line) inFIG. 2, may be utilized to provide additional air in excess of the oxidant provided by the heat engine. One of the reasons for using the supplemental air341is to control temperatures at the cathode inlet304A and the cathode outlet304B. Another reason for the supplemental air is to provide system air during the power plant start-up. As shown inFIG. 2, the supplemental air path341is provided by air blower342and optionally is pre-heated in the heat exchanger343by the cathode exhaust gas328.

Turbine exhaust gas from the expansion or turbine section330B, comprising oxidant gas suitable for use in a fuel cell, is carried by a cathode oxidant gas path324to the cathode compartment304through a cathode inlet304A. If supplemental air is used, the turbine exhaust gas is combined with the preheated supplemental air341in the cathode oxidant gas path324. After passing through the cathode304, a high-temperature cathode exhaust gas comprising spent oxidant gas is outputted from the cathode304through a cathode outlet304B into a cathode exhaust path328. This cathode exhaust gas is cooled by passing through the heat exchanger328A, which pre-heats compressed oxidant gas leaving the compression section330A of the gas turbine, and, if employed, is further cooled in the supplemental air pre-heater343, and is thereafter further cooled in the humidifying heat exchanger306C, which, as above-mentioned, pre-heats and humidifies fuel in the fuel supply path306. Cooled cathode exhaust is then exported out of the system300and may be used in further heat recovery co-generation such as combined heat and power application, steam bottoming cycle, or Organic Rankin Cycle.

As is also shown inFIG. 2, a portion of the cathode exhaust gas may be recycled back to the cathode304via a cathode recycle path326, which includes a recycle blower326A. Recycled cathode exhaust is combined with the oxidant gas in the path324before being provided to the cathode inlet304A.

As an example, the performance characteristics of a 40 MW power plant based on a Molten carbonate Fuel Cell (MCFC) hybrid system configured as inFIG. 2is presented in Table 2. Overall LHV efficiency for the conceptualized system is 61.8%.

The system330ofFIG. 2results in similar efficiencies and improvements as the system1shown inFIG. 1. The system ofFIG. 2, like the system ofFIG. 1, eliminates the need for an oxidant gas supply assembly and for a water supply assembly by using the heat engine exhaust to provide oxidant gas to the cathode and by recycling water in the anode exhaust to the fuel. In addition, the embodiment ofFIG. 2effectively recovers heat from the anode and the cathode exhaust gases produced by the fuel cell thus reducing the need for independent heating devices.

In all cases it is understood that the above-described arrangements are merely illustrative of the many possible specific embodiments which represent applications of the present invention. For example, the heat engine is not limited to the types described herein, and other devices, such as a diesel engine, may be suitable for use in the power production system. Moreover, additional components may be required to achieve a desired composition of the gas supplied to the heat engine and for optimum power production. In some cases, a steam turbine or Organic Rankine Cycle bottoming cycle system may be used in the hybrid system to recover additional heat from the fuel cell exhaust gases by using hot exhaust gases to generate steam, which is the working fluid of the steam turbine system. Numerous and varied other arrangements can be readily devised in accordance with the principles of the present invention without departing from the spirit and scope of the invention.