KR20250008677A - Reversible solid oxide cell system - Google Patents

Abstract

The present invention relates to a solid oxide battery system capable of reverse operation, in which a fuel cell mode for producing electricity using methane as fuel and a water electrolysis mode for producing methane by combining hydrogen and carbon dioxide obtained by electrolyzing water with the produced electricity are selectively driven as needed, depending on the demand for power generation, while each mode shares a hybrid tank in which methane and carbon dioxide are stored, thereby enabling efficient production and storage of energy. The present invention includes a hybrid tank in which methane and carbon dioxide are separately stored, and a reverse solid oxide battery driven in a water electrolysis mode and a fuel cell mode.

Description

{REVERSIBLE SOLID OXIDE CELL SYSTEM}

The present invention relates to a solid oxide battery system capable of reverse operation, and more specifically, to a solid oxide battery system capable of reverse operation, in which a fuel cell mode for producing electricity using methane as fuel and a water electrolysis mode for producing methane by combining hydrogen and carbon dioxide obtained by electrolyzing water with regenerative electricity are selectively driven as needed, while a hybrid tank in which methane and carbon dioxide are stored is shared by each mode, thereby enabling efficient production and storage of energy.

Recently, in line with the trend of the new climate regime, our country has established a long-term plan to gradually reduce nuclear and coal power generation and increase the share of renewable energy generation to 20% of total power generation by 2030, thereby achieving the goal of reducing greenhouse gas emissions by 37% compared to business-as-usual (BAU) levels.

However, the expansion of the proportion of renewable energy in the power grid for the government's major energy transition policy causes problems in the stability and efficiency of the power grid operation due to the imbalance between supply and demand and the limits of the power grid's capacity, which result in unused power in the power grid, which must be produced and consumed simultaneously due to the intermittent nature of major renewable energy sources such as solar and wind power and the resulting output fluctuations.

Accordingly, research on Power to Gas (P2G) technology, which produces hydrogen (H2) using electrolysis technology using unused electricity or reacts the produced hydrogen with carbon dioxide (CO2), a representative greenhouse gas, to produce methane (CH4) and use it as fuel, is being actively conducted in Europe, which has recently been leading the way in the spread of renewable energy, as a means to complement the fundamental limitations of renewable energy such as reduced stability and efficiency.

In particular, the ‘carbon dioxide methanation’ technology that utilizes carbon dioxide is a technology that is being increasingly emphasized along with the expansion of renewable energy supply because it can solve the problems of stability and efficiency deterioration of the power system due to the expansion of renewable energy supply by storing and recycling unused electricity, and at the same time, obtain the effect of reducing greenhouse gases by utilizing carbon dioxide, the main culprit of global warming.

Existing fossil fuel-based solid oxide battery technology inevitably produces carbon dioxide, which is a problem in that it does not contribute to reducing greenhouse gases. In carbon dioxide methanation technology, water is electrolyzed in water electrolysis mode to obtain hydrogen to supply the hydrogen needed to produce methane.

However, power for electrolyzing water must be supplied constantly, and renewable energy is also used to supply power. However, renewable energy is intermittent in its power generation, so it is difficult to stably start the water electrolysis mode. For this reason, an energy storage system (ESS) is added to supplement the unstable power generation of renewable energy, but this requires a huge cost.

Republic of Korea Patent Publication No. 10-1982021 (2019305.20)

The problem to be solved by the present invention is to provide a reverse-operable solid oxide battery system that is driven in a fuel cell mode that produces electricity using methane as fuel according to the demand for power generation using a reverse-operable solid oxide battery, and in a water electrolysis mode that produces methane by combining hydrogen and carbon dioxide obtained by electrolyzing water with the produced electricity, while each mode shares a hybrid tank in which methane and carbon dioxide are stored, thereby selectively supplying methane and carbon dioxide required in the fuel cell mode and the water electrolysis mode, thereby increasing the overall efficiency.

To solve the above problems, the present invention proposes a solid oxide battery system capable of reverse operation.

A solid oxide battery system of one embodiment comprises a reverse-operating solid oxide battery (rSOC) comprising a hybrid tank in which methane and carbon dioxide are stored separately with an adjustable partition; and a methane generator which produces methane by combining carbon dioxide in the hybrid tank with hydrogen produced by electrolyzing water using electricity produced in a stack in the water electrolysis mode and supplies the methane to the first zone, and a reformer which reforms methane in the hybrid tank and supplies the reformed methane to the stack in the fuel cell mode.

The above-described reverse-operation solid oxide battery of one embodiment may further include an ejector, which is provided between the methane generator and the stack in the water electrolysis mode, and mixes and compresses hydrogen of the stack and carbon dioxide of the hybrid tank and supplies them to the methane generator.

The above-described reverse-operation solid oxide battery of one embodiment may further include, in the water electrolysis mode, a water separator provided at a rear end of the methane generator to separate water from the exhaust gas of the methane generator and supply the separated water to a water tank.

The above-described reverse-operation solid oxide cell of one embodiment may further include a heater for heating water supplied from the water separator or the water tank to the stack for use in the electrolysis in the water electrolysis mode.

The above-described reverse-operation solid oxide battery of one embodiment may further include an oxygen tank for supplying and storing oxygen produced through electrolysis of water in the water electrolysis mode.

In one embodiment, the reverse-operating solid oxide cell may, in the fuel cell mode, be configured such that some of the unreacted substances contained in the exhaust gas of the stack may be recycled to the reformer, reformed, and then resupplied to the stack.

The above-described reverse-operation solid oxide cell of one embodiment may further include a burner that, in the fuel cell mode, combusts exhaust gas of the stack using oxygen in the oxygen tank as an oxidizer.

The above-described reverse-operating solid oxide cell of one embodiment further includes a water separator for separating water from combustion of the burner in the fuel cell mode, and the water separated in the water separator can be used in the water electrolysis mode of the above-described reverse-operating solid oxide cell.

In one embodiment, the reverse-operating solid oxide cell may, in the fuel cell mode, store carbon dioxide contained in the exhaust gas of the burner from which water is separated in the water separator in the hybrid tank.

In one embodiment, the reverse-operating solid oxide cell may, in the fuel cell mode, be configured such that some of the unreacted substances contained in the exhaust gas of the stack may be recycled to the stack and used as fuel.

The above hybrid tank may have variable storage capacities for methane and carbon dioxide by moving the partition.

The above-described water electrolysis mode of one embodiment may electrolyze water using an externally supplied renewable energy source, and may further include a power compensator that constantly adjusts the power supplied to the water electrolysis mode using at least one of an external power grid and a battery in which electricity produced in the fuel cell mode is temporarily stored, and the renewable energy source.

According to an embodiment of the present invention, since the electrolysis mode utilizes electricity produced from a reverse-operating solid oxide battery, a separate device for supplying electricity is not required, thereby improving energy efficiency.

According to an embodiment of the present invention, methane and carbon dioxide are stored in the same tank, and a partition capable of material transfer exists, so that the amount of methane and carbon dioxide can be easily controlled according to production and consumption demands by using them within a loop capable of reverse operation.

According to an embodiment of the present invention, the storage space inside the hybrid tank can be varied according to the amount of carbon dioxide captured in the fuel cell mode and the amount of methane produced in the water electrolysis mode.

According to an embodiment of the present invention, waste heat generated in fuel cell mode can be stored and used to generate steam in water electrolysis mode, thereby increasing heat efficiency.

Figure 1 is a diagram showing a schematic flow of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.
FIG. 2 is a drawing showing the operation of the electrolysis mode of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.
FIG. 3 is a drawing showing the operation of a fuel cell mode of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.
FIG. 4 is a diagram showing the overall flow of the water electrolysis mode and the simultaneous fuel cell mode in a solid oxide battery system capable of reverse operation according to Example 1 of the invention.

Hereinafter, several embodiments of the present invention will be described in detail using drawings. However, this is not intended to limit the present invention to any specific embodiment, and it should be understood that all transformations, equivalents, and substitutions that include the technical idea of the present invention are included in the scope of the present invention.

In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

When it is stated in this specification that a component "has" or "comprises" a sub-component, it is intended that the other component may be included, rather than excluding the other component, unless otherwise specifically stated.

The terms “Unit,” “Module,” and “Component” in this specification mean a unit that processes at least one function or operation, and may be implemented by hardware, software, or a combination of hardware and software.

The term “connected” in this specification may mean, but is not necessarily limited to, that two components are directly connected, and may also mean that the components are connected via one or more other components positioned between the components.

Figure 1 is a diagram showing a schematic flow of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.

The solid oxide battery system can be selectively operated in a fuel cell mode that produces electricity using methane as fuel, and a water electrolysis mode that produces methane by combining hydrogen obtained by electrolyzing water as a supplied energy source and carbon dioxide supplied from an external source (e.g., a hybrid tank (100)). However, since the hybrid tank where methane and carbon dioxide are stored is shared by the modes, efficient energy production and storage are possible.

The energy source supplied in the electrolysis mode here can be electricity supplied through an external power grid, or it can be a renewable energy source (or renewable electricity) produced through a power generation means that obtains power from natural forces such as wind, sunlight, river water, ocean currents, solar heat, etc.

Additionally, the electrolysis mode can be supplied from a battery (not shown in the drawing) that temporarily stores electricity produced in the fuel cell mode.

The electrolysis mode of a solid oxide battery system uses renewable energy sources (regenerative electricity) as a primary power source, but when the supply of renewable energy sources falls short of the amount of power required by the electrolysis mode, the shortfall can be supplemented from a battery storing electricity produced in the fuel cell mode or from an external power grid.

For example, if a solid oxide battery system is operated all day in electrolysis mode, it can be supplied with renewable electricity generated by solar or wind power during the day, and at night, electricity generated in advance in fuel cell mode can be supplied through stored batteries or an external power grid.

The solid oxide battery system receives carbon dioxide from a hybrid tank in a water electrolysis mode, and combines hydrogen produced by electrolyzing water supplied through regenerative electricity or an electric grid (or electricity from a battery) with the supplied carbon dioxide to produce methane, which is then stored in the hybrid tank (100). At this time, methane can be generated through a methane generator (240).

And when water is electrolyzed in the electrolysis mode, oxygen is also produced, and the oxygen can be stored in a separate oxygen tank (280) and used in the fuel cell mode.

The fuel cell mode of the solid oxide battery system produces hydrogen by reforming methane produced in the water electrolysis mode and stored in a hybrid tank (100), and produces electricity using the hydrogen.

And in the fuel cell mode, the burner (340) provided at the rear end of the stack (210) uses oxygen separated through electrolysis in the water electrolysis mode as an oxidizer to combust the exhaust gas of the stack (210). The exhaust gas combusted in the burner (340) has a high proportion of carbon dioxide and water, and these are separated, and the carbon dioxide is stored in a hybrid tank (100), and the water is stored in a water tank (270) and used when electrolyzing water in the water electrolysis mode.

The water electrolysis mode and fuel cell mode of the solid oxide battery system are explained through FIGS. 2 and 3 below.

FIG. 2 is a drawing showing the operation of the electrolysis mode of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.

As shown in Fig. 2, the system includes a hybrid tank (100) and a reverse-acting solid oxide battery (200).

A hybrid tank (100) includes a first zone (101) and a second zone (102) that are isolated from each other. The first zone (101) and the second zone (102) of the hybrid tank (100) can be divided by an adjustable partition.

Methane is stored in the first section (101) of the hybrid tank (100).

The methane stored in the first zone (101) may be methane produced in the electrolysis mode of the reverse-operating solid oxide battery (200). As a reference, a small amount of unreacted hydrogen and carbon dioxide in the electrolysis mode may also be stored in the first zone (101) of the hybrid tank (100).

If the amount of methane produced in the electrolysis mode is insufficient, the hybrid tank (100) can be supplied with external methane and supply methane to the stack (210) in the fuel cell mode.

For example, if the amount of methane produced in the electrolysis mode is insufficient, the hybrid tank (100) may be supplied with external methane through a natural gas network or a multi-gas network.

Conversely, if the amount of methane produced in the electrolysis mode is large, methane can be supplied externally through the natural gas network or multiple gas networks.

Carbon dioxide is stored in the second zone (102). In the second zone (102), carbon dioxide can be compressed and stored under high pressure.

Carbon dioxide stored in the second zone (102) is used to produce methane by combining carbon dioxide with hydrogen produced by electrolyzing water in the electrolysis mode.

The carbon dioxide may be carbon dioxide separated from the exhaust gas of the stack (210) in the fuel cell mode. For reference, a small amount of unreacted hydrogen and carbon monoxide from the exhaust gas of the stack (210) in the fuel cell mode may also be stored in the second section (102) of the hybrid tank (100).

That is, the hybrid tank (100) supplies carbon dioxide in the second zone (102) to the reverse operating solid oxide cell (200) to be used for the methanation reaction in the electrolysis mode of the reverse operating solid oxide cell (200) and stores methane produced by the methanation reaction in the first zone (101). In addition, the hybrid tank (100) supplies methane in the first zone (101) to be used as fuel in the fuel cell mode of the reverse operating solid oxide cell (200) and stores carbon dioxide, which is one of the products of the stack (210), in the second zone (102).

The hybrid tank (100) may also supply carbon dioxide to the outside through a multi-gas network or carbon dioxide supply network when the amount of carbon dioxide stored in the fuel cell mode is greater than the capacity of the hybrid tank (100).

Conversely, the hybrid tank (100) may be supplied with carbon dioxide from outside through a multi-gas network or carbon dioxide supply network if the amount of carbon dioxide stored in the fuel cell mode is less than the capacity of the hybrid tank (100).

Meanwhile, the first zone (101) and the second zone (102) of the hybrid tank (110) may be partitioned with adjustable partitions.

The partitions of the hybrid tank (110) vary the storage capacity of the first zone (101) and the second zone (102).

For example, the partition of the hybrid tank (110) may reduce the capacity of the second zone (102) instead of increasing the capacity of the first zone (101) when the production of methane is high in the electrolysis mode.

Additionally, the partition of the hybrid tank (110) may reduce the capacity of the second zone (102) instead of increasing the capacity of the first zone (101) when the capacity of carbon dioxide captured in fuel cell mode is low.

The reversible solid oxide cell (200) (rSOC) may have different operating configurations depending on the electrolysis mode and fuel cell mode, and the description will focus on the configuration operating in the electrolysis mode.

The reverse-acting solid oxide battery (200) includes a stack (210), a first water separator (220), a first ejector (230), a methane generator (240), a second water separator (250), a compressor (260), a water tank (270), and an oxygen tank (280).

In electrolysis mode, the stack (210) electrolyzes pure water using electrical energy supplied from the electric grid to produce hydrogen and oxygen.

For example, the water electrolysis mode can electrolyze water using electricity supplied from an external power grid, or can electrolyze water using regenerative electricity produced by power generation means that obtain power from natural forces such as wind, solar energy, river water, ocean currents, and solar heat, or can electrolyze water using electricity supplied from a battery (not shown in the drawing) that temporarily stores electricity produced in the fuel cell mode.

The electrolysis mode operates at temperatures where high-temperature electrolysis can occur between 500 and 850 °C.

In a reverse-acting solid oxide battery (200), water vapor flows into the fuel electrode as a reactant, and when voltage is applied to the anode, a decomposition reaction of the water vapor occurs, causing water molecules to react and separate into hydrogen and oxygen.

The reverse-acting solid oxide battery (200) supplies oxygen obtained through electrolysis of water to an oxygen tank (280) through an oxygen electrode output terminal, and supplies hydrogen to a first hydrogen separator (220) located at the rear end of the hydrogen electrode output terminal.

Since the electrolysis mode uses electricity produced in the fuel cell mode of the reverse-operating solid oxide battery (200), no device for supplying electricity is required, thereby improving energy efficiency.

The first water separator (220) separates some of the water contained when hydrogen is supplied from the stack (210).

The water separated in the first water separator (220) is recycled to the stack (210) and electrolyzed. A heater (not given a drawing symbol) may be further provided to heat the water recycled from the first water separator (220) to the stack (210) into steam.

The first ejector (230) receives hydrogen from the stack (210) through the first hydrogen separator (220) and carbon dioxide from the hybrid tank (100) and mixes them.

Hydrogen and carbon dioxide mixed in the first ejector (230) are compressed and supplied to the methanation generator (240). For reference, a high pressure state is required for the methanation reaction of the methanation generator (240), and the first ejector (230) can reduce the compression force required before the methanation reaction by using the pressure of carbon dioxide stored at high pressure in the hybrid tank (100).

The methane generator (240) generates methane by combining supplied carbon dioxide and hydrogen.

The technology for converting carbon dioxide into methanogen in a methanogen generator (240) uses a thermochemical methanation reaction using a nickel-based solid catalyst or a biological methanation reaction using microorganisms, depending on the type of catalyst that reacts carbon dioxide and hydrogen.

Thermochemical methanation reaction requires maintenance of high operating pressure (10 bar~) and temperature (300~550℃) for thermochemical catalytic reaction. For reference, the operating pressure can utilize the pressure of high-pressure carbon dioxide of the hybrid tank (100) or can use a separate compressor.

When a methanation reaction is performed using a Ni, Co, or Ni-Co catalyst, H2O generated in the methanation reaction may cause a water gas shift reaction at high temperature to generate carbon dioxide in addition to methane, and the generated carbon dioxide may be stored in the first section (101) of the hybrid tank (100) where methane is stored.

Biological methanation is a process that uses microorganisms that produce methane for the reaction of carbon dioxide and hydrogen as biocatalysts. Compared to thermochemical methanation technology, it has high energy efficiency due to its operating characteristics such as relatively low operating pressure (0–10 bar) and temperature (20–70°C).

The second water separator (250) separates water from the methane produced in the methane generator (240). As a reference, since the methane gas discharged from the methane generator is at a high temperature, a cooling process may be performed before being supplied to the second water separator (250).

The water separated in the second water separator (250) is recycled to the stack (210) and electrolyzed. A heater (not given a drawing symbol) may be additionally provided to heat the water recycled from the second water separator (250) to the stack (210) into steam.

The compressor (260) compresses methane from which moisture has been separated in the second water separator (250). The moisture compressed in the compressor (260) goes through a cooling process and is stored in the hybrid tank (100).

The water tank (270) supplies water for electrolysis in the stack (210). The water stored in the water tank (270) may be water separated from the exhaust gas of the stack (210) in the fuel cell mode as described above. The water tank (270) may supply water for electrolysis to the stack (210) in the water electrolysis mode, and a heater (not given a drawing symbol) for heating the water supplied from the water tank (270) may be provided between the water tank (270) and the stack (210).

The oxygen tank (280) stores oxygen produced by electrolyzing water in electrolysis mode.

Oxygen from the oxygen tank (280) can be supplied to a burner (340) provided at the rear end of the stack (210) in fuel cell mode and used as an oxidizer required for combustion.

Meanwhile, the solid oxide battery (200) may further include a power compensator (not shown in the drawing).

The power compensator regulates the power supply to the renewable energy source (regenerated electricity) and the external power grid or battery so that electrolysis can be smoothly performed in the water electrolysis mode of the solid oxide cell (200). As a reference, the electricity produced in the fuel cell mode is temporarily stored in the battery.

In one embodiment, the power compensator controls the output of the energy source so that the renewable energy source can be used preferentially in the electrolysis mode via the power grid, but if the supply of the renewable energy source falls short of the amount of power required in the electrolysis mode, the shortfall can be supplemented from the power grid (or battery) and used. In this sense, the power compensator may be considered as a controller (not shown in the drawing) of the solid oxide battery (200).

Meanwhile, the solid oxide battery (200) may further be equipped with a heat tank (drawing symbol not given).

The heat tank can store the heat of the air electrode exhaust gas in the fuel cell mode of the solid oxide cell (200) or can be utilized in the water electrolysis mode.

The heat source stored in the heat tank can be used to convert water into steam in electrolysis mode. In addition, the heat source stored in the heat tank can also supplement the heat source required in other configurations.

FIG. 3 is a drawing showing the operation of a fuel cell mode of a solid oxide battery system capable of reverse operation according to Example 1 of the present invention.

As shown in Fig. 3, the system includes a hybrid tank (100) and a reverse-acting solid oxide battery (200).

The hybrid tank (100) is identical to the hybrid tank (100) of Fig. 2, so redundant description is omitted.

The reverse-operating solid oxide cell (200) (rSOC, REVERSIBLE SOLID OXIDE CELLS) will be described mainly with respect to the configuration operated in fuel cell mode.

The reverse-acting solid oxide battery (200) includes a third ejector (310), a reformer (320), a fourth ejector (330), a stack (210), a burner (340), a third water separator (350), and a water tank (270).

The third ejector (310) mixes methane supplied from the hybrid tank (100) with gases of the methane, hydrogen, carbon dioxide, carbon monoxide, and moisture series recycled from the exhaust gas of the stack (210). The third ejector (310) supplies the mixed gas to the reformer (320). The third ejector (310) provides the steam-to-carbon ratio required for the reformer (320) through the exhaust gas of the recycled stack (210).

The reformer (320) reforms the supplied methane series fuel to produce hydrogen.

A Ni-based catalyst is used as a catalyst in the reformer (320), and it plays a role in suppressing coke formation (or carbon deposition) due to reforming of higher hydrocarbons by decomposing C2+ hydrocarbons contained in the reaction raw material (or fuel) into CH4, CO, H2, etc. Coke formation is related to the amount of steam and is determined by the steam-to-carbon ratio (S/C). If the value of S/C is too low, the possibility of coke formation increases.

In the reformer (320), the reformate fuel is converted into H2 through direct internal reforming, i.e., steam methane reforming reaction and water-gas shift reaction, at the fuel electrode of the stack (210). The H2 produced in this way is converted into electricity through an electrochemical reaction.

Hydrogen produced by reforming in the reformer (320) is supplied to the stack (210) via the fourth ejector (330). For reference, the exhaust gas of the reformer (320) may contain a small amount of unreacted carbon monoxide, carbon dioxide, methane, and moisture in addition to the produced hydrogen.

The fourth ejector (330) mixes the exhaust gas of the reformer (320) with the methane series gas recycled from the exhaust gas of the stack (210) and supplies it to the fuel electrode of the stack (210). Since the fourth ejector (330) mixes the recycled exhaust gas of the stack (210) with the reformed gas (fuel), a heat exchanger required to heat the fuel supplied to the stack (210) is not required, thereby increasing efficiency in terms of power usage and cost.

The stack (210) includes an anode having an anode input and an anode output and a cathode having a cathode input and a cathode output.

The stack (210) receives heated external air (Air) as an air electrode and receives heated fuel as a fuel electrode.

For example, preheated air is supplied to the cathode, oxygen ions generated at the cathode move to the fuel electrode through the electrolyte, and an electrochemical reaction of H2 and O2 occurs at the triple-phase boundary of the cathode, and electricity is generated through this reaction.

The high temperature exhaust gas discharged from the air electrode of the stack (210) can be used to heat the air input to the air electrode through a heat exchanger and then cooled and discharged to the outside.

Some of the fuel electrode exhaust gas of the stack (210) is branched to the third ejector (310) and the fourth ejector (330), and the remainder is supplied to the burner (340) and burned.

The burner (340) combusts the fuel electrode exhaust gas of the stack (210) using oxygen supplied from the oxygen tank (280). For reference, the oxygen of the oxygen tank (280) is oxygen produced by electrolysis of water in the water electrolysis mode of the reverse-operating solid oxide cell (200).

For example, the exhaust gas coming out through the fuel electrode outlet of the stack (210) contains products such as CO2 and H2O and unreacted fuels such as H2, CO, and CH4. Unreacted fuels such as H2 and CO become CO2 and H2 becomes H2O in the process of being combusted with oxygen in the burner (340). As a result, the exhaust gas of the burner (340) may have a high proportion of CO2 and H2O and a small amount of unreacted H2 and CO may remain.

The combustion heat generated from the burner (340) may be stored in a heat tank (not shown). The heat stored in the heat tank may be used to heat water supplied to the stack (210) in the water electrolysis mode and convert it into steam.

The third water separator (350) separates moisture from the combustion gas of the burner (340).

The third steam separator (350) can use either a centrifugal steam separator or a reverse steam separator. The centrifugal steam separator separates moisture by swirling the steam in a cyclone separator and the centrifugal force. The reverse steam separator separates moisture by rapidly changing the direction of steam flow using a baffle plate, etc.

The combustion gas of the burner (340) becomes a CO2 rich state with a high proportion of carbon dioxide because most of the moisture is removed while passing through the water separator. For reference, the combustion gas of the burner (340) may contain a small amount of H2 and CO while having a high proportion of carbon dioxide. The small amount of H2 and CO may also be stored in the hybrid tank (100).

The combustion gas of the water-separated burner (340) is compressed and cooled, then stored in the second section (102) of the hybrid tank (100), and supplied for methanation reaction in the water electrolysis mode.

The water tank (270) stores the water separated from the water separator. The water stored in the water tank (270) is supplied as steam for electrolysis in the water electrolysis mode after going through a heating process.

FIG. 4 is a diagram showing the overall flow of the water electrolysis mode and the simultaneous fuel cell mode in a solid oxide battery system capable of reverse operation according to Example 1 of the invention.

Referring to Fig. 4, the electrolysis mode will first be described. Water (0.134 mol/s) supplied from a water tank (270) is heated to 25 to 750°C in a heater and then supplied to a stack (210) to perform an electrolysis reaction. For reference, the stack (210) operates at 1 bar, the input-side temperature of the water vapor is approximately 750°C, and the output-side temperature is approximately 745°C.

The stack (210) obtains hydrogen and oxygen by electrolyzing water using the supplied energy source.

For example, the electricity required for electrolysis by the stack (210) may be electricity supplied through an external power grid, or may be an energy source (regenerative electricity) produced by a power generation means that obtains power from natural forces such as wind, solar energy, river water, ocean currents, solar energy, etc. In addition, the stack (210) may be supplied from a battery (not shown in the drawing) that temporarily stores electricity produced in fuel cell mode.

For these technical features, the present embodiment may further include a power compensator. The power compensator regulates the power supply to a renewable energy source (regenerated electricity) and an external power grid or battery so as to facilitate electrolysis in the water electrolysis mode of the solid oxide battery (200).

In one embodiment, the power compensator controls the output of the energy source so that the renewable energy source can be used preferentially in electrolysis mode via the power grid, but if the supply of the renewable energy source falls short of the amount of power required in electrolysis mode, the shortfall can be supplemented from the power grid (or battery).

The oxygen produced by electrolyzing water in the stack (210) is discharged to the anode side and then first cooled from 745°C to 120°C (duty = 10.46 kW) and secondarily cooled from 120°C to 25°C (load = 0.17 kW). Some of it is stored in the oxygen tank (280), and some of it is recycled to the input of the stack (210) via a blower (duty = 0.425 kW, 1-1.2 bar) and a heater (duty = 9.16 kW, 130-750°C).

After the steam is electrolyzed inside the stack (210), the exhaust gas on the output side of the cathode contains H2 and a small amount of steam. The exhaust gas (H2, a small amount of steam) of the stack (210) is cooled in a cooler to lower the temperature from 745°C to 50°C and release 2.81 kW of heat.

The exhaust gas (H2, a small amount of steam) of the first cooled stack (210) is additionally cooled from 50°C to 25°C, releasing 0.56 kW of heat, and about 0.014 mol/s of water is condensed in the first steam separator (220) and recycled again to be supplied as an input to the stack (210).

The exhaust gas of the stack (210) from which moisture is separated by the first water separator (220) contains H2, and the first ejector (230) mixes the H2 contained in the exhaust gas of the stack (210) with the 0.032 mol/s high-pressure CO2, CO supplied from the hybrid tank (100).

In the first ejector (230), the pressure of the mixture (CO2, CO, H2) increases from 1 bar to 6 bar, and then passes through a compressor (drawing symbol not given) where the pressure increases from 6 bar to 15 bar.

The high-pressure mixture with increased pressure is supplied to the methanogen (240), where CO2 and H2 react at 280°C to produce CH4. For reference, the methanation reaction is an exothermic reaction and can release 4.91 kW of heat at 280°C. The exhaust gas of the methanogen (240) may contain a small amount of H2 and CO2 in addition to the products CH4 and H2O. The H2 and CO2 may also be stored in the hybrid tank (100).

The second water separator (250) cools the exhaust gas of the methane generator (240) from 280°C to 178°C (duty = 0.39 kW) to condense water, and further cools it to 178 to 25°C (duty = 3.18 kW) to condense the water. Approximately 0.058 mol/s of water is condensed in the second water separator (250) and recycled to the cathode side input of the stack (210) for water electrolysis in the stack (210). Since the water is recycled by the first water separator (220) and the second water separator (250), the water usage of the water tank (270) can be reduced to 0.062 mol/s.

The methane gas of the second separator (250) is compressed from 15 bar to 75 bar through a compressor (drawing symbol not given). At this time, 0.25 kW of power can be consumed. The compressed methane gas is cooled from 207°C to 25°C in a cooler (duty = 0.26 kW) and then stored in a hybrid tank (100).

Meanwhile, the reverse-acting solid oxide battery (200) may be further equipped with an electric heater. The electric heater may have a power consumption of 0.28 kW. The electric heater may be used to heat oxygen input to the anode side of the stack (210) or to further heat vapor supplied to the cathode side of the stack (210).

Fuel cell mode operates when power demand is required.

Methane and a small amount of carbon and hydrogen stored in the hybrid tank (100) are heated from 25°C to 230°C under 75 bar conditions through a heater before being supplied to the reformer (320) (load = 0.16 kW). Then, the heated methane gas is supplied to the reformer (320) which reduces the pressure from 75 bar to 15 bar through a turbine and operates at a pressure of 8.5 bar.

For reference, in the case of partial external reforming, the temperature is 550°C, and the maximum internal reforming ratio that the stack (210) can handle is about 0.9, so the optimal external steam methane reforming ratio is 0.1. Considering the endothermic nature of methane reforming, the higher the internal reforming ratio, the less air is required to cool the stack (210), and by operating the reformer (320) at high pressure, a low external reforming ratio can be obtained, and the cost of the special catalyst used for steam methane reforming can be reduced.

The mixed gas supplied from the reformer (320) to the stack (210) includes CH4, H2, CO2, H2O, and CO. And the stack (210) produces 10 kW of power using the mixed gas as fuel.

For reference, the fuel utilization rate of the stack (210) can be set to 0.85, the input temperature of the stack (210) is about 710°C, and the output temperature of the stack (210) is a high temperature of about 810°C. The exhaust gas coming out through the fuel electrode outlet of the stack (210) includes products such as CO2 and H2O and unreacted fuels such as H2, CO, and CH4, and is recycled to the third ejector (310) equipped in front of the reformer (320) and the fourth ejector (330) equipped in the rear of the reformer (320).

The third ejector (310) mixes methane supplied from the hybrid tank (100) with methane-based gas recycled from the exhaust gas of the stack (210). The third ejector (310) supplies the mixed gas to the reformer (320). In addition, the third ejector (310) provides the steam-to-carbon ratio required for the reformer (320).

Since the fourth ejector (330) mixes the exhaust gas of the recycled stack (210) with the reformed gas (fuel), a heat exchanger required to heat the fuel supplied to the stack (210) is not required, thereby increasing power usage and cost efficiency.

The high temperature exhaust gas discharged from the air electrode of the stack (210) can be used to heat the air input to the air electrode through a heat exchanger and then cooled and discharged to the outside.

Specifically, the cathode side exhaust gas (0.98 mol/s) of the stack (210) provides 23.77 kW of heat through heat exchange with fresh air supplied to the cathode input of the stack (210) and is heated from about 35°C to about 710°C. Then, the heat-exchanged exhaust gas of the stack (210) is finally cooled from 126°C to 50°C (load = 2.48 kW) before being exhausted to the outside.

The remaining air electrode gas is then cooled from 810°C to 90°C (duty = 1.54 kW) and then further cooled from 90°C to 25°C (duty = 1.63 kW) to condense water at a rate of 0.033 mol/s in the steam-water separator.

The burner (340) combusts the fuel electrode exhaust gas of the stack (210) using oxygen supplied from the oxygen tank (280). For reference, the oxygen of the oxygen tank (280) is oxygen produced by electrolysis of water in the water electrolysis mode of the reverse-operating solid oxide cell (200).

For example, the exhaust gas coming out through the fuel electrode outlet of the stack (210) contains products such as CO2 and H2O and unreacted fuels such as H2, CO, and CH4. In the process of combustion of unreacted fuels such as H2 and CO with oxygen in the burner (340), CO becomes CO2 and H2 becomes H2O. As a result, the exhaust gas of the burner (340) has a high proportion of CO2 and H2O and a small amount of unreacted H2 and CO remains.

The third water separator (350) separates moisture from the combustion gas of the burner (340).

The combustion gas of the burner (340) becomes a CO2 rich state with a high proportion of carbon dioxide because most of the moisture is removed while passing through the water separator. For reference, the combustion gas of the burner (340) may contain a small amount of H2 and CO while having a high proportion of carbon dioxide. The small amount of H2 and CO may also be stored in the hybrid tank (100).

Before the combustion gas of the burner (340) from which moisture has been separated is stored in the hybrid tank (100), the pressure of the combustion gas from which moisture has been separated is increased from 1 bar to 75 bar using a compressor and a cooler. The combustion gas of the burner (340) from which moisture has been separated is compressed, cooled from 150°C to 25°C, and then stored in the hybrid tank (100).

The overall efficiency of a reversible solid oxide battery system is 64.2%, but by using 4.06 kW of waste heat at 270°C, 0.3 kW of waste heat at 100°C, and about 3.4 kW of waste heat at 700°C, the system efficiency can be improved to 78%.

Although the present invention has been described above with reference to several embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

100: Hybrid Tank
200: Reverse-acting solid oxide battery
210: Stack
220: 1st Rider Separator
230: 1st Ejector
240: Methane Generator
250: 2nd float separator
260: Compressor
270: Water Tank
280: Oxygen Tank

Claims (12)

A hybrid tank in which methane and carbon dioxide are stored separately with adjustable partitions; and
A reverse-operable solid oxide cell system (including rSOC) comprising a methane generator which produces methane by combining hydrogen produced by electrolyzing water using carbon dioxide of the hybrid tank and electricity produced in the stack in the electrolysis mode and supplies the methane to the first zone, and a reformer which reforms methane of the hybrid tank in the fuel cell mode and supplies the reformed methane to the stack. In the first paragraph,
The above-mentioned reverse-operation solid oxide battery, in the above-mentioned water electrolysis mode,
An ejector provided between the methane generator and the stack, which mixes and compresses hydrogen from the stack and carbon dioxide from the hybrid tank and supplies them to the methane generator.
A solid oxide battery system capable of reverse operation further comprising: In the first paragraph,
The above-mentioned reverse-operation solid oxide battery, in the above-mentioned water electrolysis mode,
A water separator installed at the rear end of the above methane generator, which separates water from the exhaust gas of the above methane generator and supplies it to a water tank.
A solid oxide battery system capable of reverse operation further comprising: In the third paragraph,
The above-mentioned reverse-operation solid oxide battery, in the above-mentioned water electrolysis mode,
A heater for heating water supplied from the water separator or the water tank to the stack for use in the electrolysis.
A solid oxide battery system capable of reverse operation further comprising: In the first paragraph,
The above-mentioned reverse-operation solid oxide battery, in the above-mentioned water electrolysis mode,
An oxygen tank that supplies and stores oxygen produced through the electrolysis of the water above.
A solid oxide battery system capable of reverse operation further comprising: In the first paragraph,
The above-mentioned reverse-operation solid oxide cell, in the fuel cell mode,
A reverse-operable solid oxide battery system in which some of the unreacted substances contained in the exhaust gas of the stack are recycled to the reformer, reformed, and then resupplied to the stack. In paragraph 5,
The above-mentioned reverse-operation solid oxide cell, in the fuel cell mode,
A burner that burns the exhaust gas of the stack using the oxygen in the oxygen tank as an oxidizer.
A solid oxide battery system capable of reverse operation further comprising: In Article 7,
The above-mentioned reverse-operation solid oxide cell, in the fuel cell mode,
Further comprising a water separator for separating water from the combustion gas of the above burner,
A reverse-operable solid oxide battery system, characterized in that the water separated in the above-mentioned water separator is used in the water electrolysis mode of the above-mentioned reverse-operable solid oxide battery. In Article 8,
The above-mentioned reverse-operation solid oxide cell, in the fuel cell mode,
A reverse-operable solid oxide battery system, characterized in that carbon dioxide contained in the exhaust gas of the burner from which moisture is separated in the above-mentioned water separator is stored in the above-mentioned hybrid tank. In the first paragraph,
The above-mentioned reverse-operation solid oxide cell, in the fuel cell mode,
A reverse-operable solid oxide battery system, characterized in that some of the unreacted substances contained in the exhaust gas of the stack are recycled to the stack and used as fuel. In the first paragraph,
The above hybrid tank,
A reverse-operable solid oxide battery system characterized in that the storage capacity of the methane and carbon dioxide is variable through movement of the partition. In the first paragraph,
The above electrolysis mode electrolyzes water using an externally supplied renewable energy source.
A power compensator that constantly adjusts the power supplied to the water electrolysis mode by using at least one of an external power grid and a battery in which electricity produced in the fuel cell mode is temporarily stored and the renewable energy source.
A solid oxide battery system capable of reverse operation further comprising: