Patent Application
20250105316
The present disclosure concerns a high efficiency power solution by integration of pressurized solid oxide fuel cell with turbomachinery. More specifically, the present disclosure concerns a system in which the compressor produces pressurized air for a solid oxide fuel cell and hot exhaust gas from the solid oxide fuel cell is expanded in the power recovery expander. The system is configured to operate with different types of expanders, including hot gas expanders, turbo expanders, low pressure expanders.
Embodiments disclosed herein specifically concern solid oxide fuel cell systems integrated with turbomachinery wherein each unit can operate individually from one another. According to the embodiments disclosed herein the compression system upstream the solid oxide fuel cell is a combination of an electric motor driven centrifugal or a reciprocating low pressure compressor and a high pressure compressor driven by a power recovery expander.
It is known that a fuel cell extracts work directly from the chemical potential energy, so that it can be used to bypass the entropy-generating combustion process which is predominant in a gas turbine.
In particular, solid oxide fuel cells (SOFCs) are energy conversion devices that produce electricity by electrochemically combining a fuel and an oxidant across an ionic conducting oxide electrolyte. The dense electrolyte is sandwiched between two porous electrodes, the anode and the cathode (the anode/electrolyte/cathode sandwich is referred to as a single cell). Fuel is fed to the anode, undergoes an oxidation reaction, and releases electrons to an external circuit. Oxidant is fed to the cathode, accepts electrons from the external circuit, and undergoes a reduction reaction. The electron flow in the external circuit from the anode to the cathode produces direct-current electricity. SOFCs operate at about 700 to 1000° C. under atmospheric or pressurized conditions depending on specific cell configurations and system designs.
In particular, it is well-known that SOFCs generate more power at higher pressure and temperature. Hence, an increase in operating pressure leads to a corresponding increase in power output from the SOFC for the same amount of fuel consumed. In order to achieve this result, a compressor at the inlet of the SOFC is required to pressurize the incoming air. However, SOFCs are not able to completely utilize the entire feed fuel. The unutilized fuel can be subjected to combustion downstream the SOFC, thereby raising exhaust streams enthalpy, that can be further recovered by means of expansion by integration of fuel cell with turbomachinery. Thus, electrical power is produced by both the solid oxide fuel cell generator and the turbine. For this reason, combining high efficiency of pressurized SOFCs with turbomachinery products has become an area of interest in order to reduce the overall fuel consumption for generating the same power.
U.S. Pat. No. 5,413,879A discloses an integrated gas turbine solid oxide fuel cell system in which a compressor produces compressed air that is pre-heated and then supplied to a solid oxide fuel cell generator. The solid oxide fuel cell generator, which is also supplied with a first stream of fuel, produces electrical power and a hot gas. In the solid oxide fuel cell generator, the unreacted portion of the fuel is combusted with oxygen remaining in the hot gas to further heat the hot gas. To fully utilize the potential of the exhaust stream, still at a high temperature, the further heated hot gas is then directed to a topping combustor that is supplied with a second stream of fuel so as to produce a still further heated hot gas that is then expanded in a turbine.
However, addition of excess fuel to generate surplus power from the turbine reduces the efficiency of such a system. Nevertheless, it cannot be avoided because the turbine has to run at its rated power while simultaneously driving the compressor.
As a result, the combined system according to the prior art is mechanically coupled as the compressor and power turbine in the unit are linked with one another. As such, it would be difficult to operate always at optimum conditions with respect to both the gas turbine and the SOFC.
Accordingly, an improved method of integrating solid oxide fuel cell with turbomachinery to address the efficiency limitation and coupling of the systems of the current art would be beneficial and would be welcomed in the technology. Further, an improved system to address the issues of addition of excess fuel thereby an additional combustor to generate surplus power from the turbine would also be welcomed. More in general, it would be desirable to provide an improved method of integrating solid oxide fuel cell with turbomachinery adapted to more effectively address the problems entailed by integrated gas turbine solid oxide fuel cell systems according to the prior art by offering higher efficiency thereby reducing the operative expense (OPEX) of the system on a long run while simultaneously reducing carbon emissions per kW.
In one aspect, the subject matter disclosed herein is directed to a solid oxide fuel cell system comprising a fuel feed line and an oxidant gas feed line with an oxidant gas compression system upstream the solid oxide fuel cell, an exhaust gas line downstream said solid oxide fuel cell, a heat exchanger configured to allow heat exchange between said exhaust gas on the hot side of said heat exchanger and said oxidant gas and fuel on the cold side of said heat exchanger and an expansion system configured to expand said exhaust gas downstream said heat exchanger, wherein the oxidant gas compression system comprises a low pressure compressor, driven by an electric motor and a high-pressure compressor, driven by said expansion system by means of a common shaft.
According to another aspect, a combustion chamber is arranged downstream said solid oxide fuel cell, to combust unreacted fuel and oxidant gas. The combustion chamber can be integral to or separate from said solid oxide fuel cell.
According to yet another aspect, the expansion system comprises an expander.
Alternatively, the expansion system comprises a high-pressure expander and a low pressure expander, configured to expand said exhaust gas downstream said heat exchanger, an additional heat exchanger being configured to allow heat exchange between the exhaust gas from the heat exchanger upstream the high-pressure expander on the hot side of the second heat exchanger and an exhaust gas stream downstream said high-pressure expander; and a low pressure expander configured to expand the exhaust stream downstream the second heat exchanger. In particular, the low pressure expander can be connected to the high pressure expander and to the high-pressure compressor by means of a common shaft.
In particular, according to one aspect, the oxidant gas for reaction in the solid oxide fuel cell is air.
A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
According to one aspect, the present subject matter is directed to a solid oxide fuel cell system integrated with turbomachinery to provide a high efficiency power generation solution. In particular, this aim is achieved by combining a two stage compression-SOFC system with one or more expanders at the outlet of the fuel cell to further recover the energy present in the high pressure, high temperature exhaust of SOFC. The proposed combination offers higher efficiency when compared with conventional power generation systems thereby reducing the operative expense (OPEX) of the system on a long run while simultaneously reducing the carbon emissions per kW.
According to one aspect, the proposed subject matter allows to cope with increasing future energy demand for both industrial and micro grid applications while respecting more stringent emission norms.
According to one aspect, the proposed subject matter offers high efficiency over a wide range of operating pressures and can cater to both industrial and microgrid applications. This would mean same power can be produced by considerably lower fuel, which also translates to lower emissions.
According to one aspect, the proposed subject matter is more efficient at lower pressures when compared to integrated gas turbine SOFC systems because it takes advantage of the fact that additional power demanded by compression when supplied by an electric motor is more efficient than by fuel addition at lower pressures.
According to another aspect, the proposed subject matter is also compatible with lower mass flow rates and is capable to work in lower power ranges, making it an attractive offering for microgrid applications.
According to still another aspect, since exhaust gas temperature from SOFC can be higher than the temperature limit of some low power expanders, a different configuration is needed to control the expander inlet temperature. According to this configuration, a heat exchanger is provided to lower the temperature of the exhaust stream from the SOFC and directed to the first expander by exchanging heat with the outlet stream from the first expander. The outlet stream enthalpy from first expander is thus consequently increased after heat exchanger and can be further recovered by means of a second expander.
Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
When introducing elements of various embodiments, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Referring now to the drawings,
While in the schematic of
While in the schematic of
According to the present disclosure, the first embodiment shall always include:
Additionally, according to the present disclosure, solid oxide fuel cell can be replaced by any fuel cell which is adapted to operate at similar pressure and temperature conditions at similar or higher efficiencies.
The solid oxide fuel cell system integrated with turbomachinery shown in
With continuing reference to
Under this example, a maximum inlet pressure of 4 bara was imposed as operating limit for the expander 5, this value being a structural limitation of many high gain expanders on the market.
According to this example, the SOFC 7 parameters were the following:
The operating parameters of the electric motor 2 driven low pressure compressor 3 were the following:
The operating parameters of the high pressure compressor 4 were the following:
The operating parameter of the expander 5 were the following:
The operating parameter of the heat exchanger 6 were the following:
Always with continuing reference to
The fuel consumption and corresponding powers for the components in example 1 were derived from the above assumptions and are as follows:
The resulting efficiency of this integrated system of example 1 being equal to 60.42%.
From the above example it is evident that a system as the one defined according to the present disclosure for a power range up to 10 MW can function utilizing the exhaust of a fuel cell to further recover energy through an expander thereby further increasing the overall efficiency of the system. In the absence of this integration of an expander with the fuel cell, the power required to compress air would be derived from the fuel cell, thus reducing the system efficiency. The efficiency of the system increases with pressure up to an optimum pressure and remains constant thereafter. The change in efficiency of the system from the above example up to a pressure of 10 bar can be verified in a range of 60.42% to 63.5%. After an efficiency of 63.5% is achieved, then the efficiency remains constant with substantial impact on materials, with the need of selecting high pressure resistant materials.
With continuing reference to
According to this example, the SOFC 7 parameters were the following:
The operating parameter of the electric motor 2 driven low pressure compressor 3 were the following:
The operating parameter of the high pressure compressor 4 were the following:
The operating parameter of the expander 5 were the following:
The operating parameter of the heat exchanger 6 were the following:
Always with continuing reference to
The fuel consumption and corresponding powers for the components in example 2 were derived from the above assumptions and are as follows:
The resulting efficiency of this integrated system of example 2 being equal to 58.8%
From the above example it is evident that a system as the one defined according to the present disclosure for a power range up to 1 MW for microgrid applications can function utilizing the exhaust of a fuel cell to further recover energy through an expander thereby further increasing the overall efficiency of the system. In the absence of this integration of an expander with the fuel cell, the power required to compress air would be derived from the fuel cell, thus reducing the system efficiency. The efficiency of the system increases with pressure up to an optimum pressure and remains constant thereafter. The lower efficiency for low power application is due to lower isentropic efficiency of the expanders selected in the power range. The change in efficiency of the system from the above example up to a pressure of 7 bar can be verified in a range of 58.8 to 60.5%.
Referring now to
According to this second embodiment, a second heat exchanger 28 is arranged on the SOFC system exhaust line 37, upstream the high-pressure expander 25 and is configured to allow lowering the temperature of the high pressure exhaust stream 37 from the heat exchanger 26 by exchanging heat with the exhaust gas stream 39 from the high-pressure expander 25. This configuration is needed when the temperature of SOFC exhausts after heat exchange with air and fuel directed to the SOFC system 21 is still higher than typical temperature limitations on low power expanders and inlet temperature is a constraint for the expander designs. Finally, a low pressure expander 29 is arranged on the exhaust stream 40, downstream the heat exchanger 28 to further recover available energy. The low pressure expander 29 is connected to the high pressure expander 25 and to the high-pressure compressor 24 by means of a common shaft. Splitting the expansion in two stages also allows using the SOFC exhaust to heat the low temperature exhaust 39 of the high pressure expander 25, thus increasing the efficiency of the system when single stage expansion is not possible due to the constraint of high inlet temperature.
While in the schematic of
According to the present disclosure, the second embodiment shall always include:
Additionally, according to the present disclosure, solid oxide fuel cell can be replaced by any fuel cell which is adapted to operate at similar pressure and temperature conditions at similar or higher efficiencies.
The solid oxide fuel cell system integrated with turbomachinery shown in
With continuing reference to
Under this example, a pressure of 10 bara was applied to the SOFC system 21.
According to this example, SOFC 21 parameters were the following:
The operating parameter of the electric motor 22 driven low pressure compressor 23 were the followings:
The operating parameter of the high pressure compressor 24 were the followings:
The operating parameter of the high pressure expander 25 were the followings:
The operating parameter of the low pressure expander 29 were the followings:
Always with continuing reference to
The fuel consumption and corresponding powers for the components in example 3 were derived from the above assumptions and are as follows:
The resulting efficiency of this integrated system of example 3 being equal to 53.7%.
The example is applicable in case of challenges in dealing with high exhaust temperature from SOFC or high inlet temperatures at expanders. According to this embodiment of the present disclosure an intercooling heat exchanger is introduced, allowing to reduce the temperature of the feed to the high pressure expander 25. The changes in efficiency of the system is attributed to additional equipment pressure losses leading to lower enthalpy available for expansion.
While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing from the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022000001484 | Jan 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/025036 | 1/25/2023 | WO |
