JPH04206158A - Separation-recovery of carbon dioxide by use of molten carbonate type fuel cell and device thereof - Google Patents

Abstract

PURPOSE:To separate and recover carbon dioxide simply and efficiently by using a molten carbonate type fuel cell, making noncombustible gas flow containing the carbon dioxide required to be removed into the air electrode side, consuming completely an active material for electrochemical reaction by controlling electric current volume or gas flow rate, and obtaining gas rich in the carbon dioxide. CONSTITUTION:Reformed gas 102 came out from a reformer 2 is supplied to fuel electrodes 3a and 3b in fuel cell groups 1a and 1b. The cell groups 1a and 1b are connected electrically in series, and the cell group 1b is operated so that consumption of water and carbon monoxide in the cells fixed exclusively against load current flowing in the 1b and flow rate of the water and the carbon monoxide contained in the gas 102 supplied to the cell group 1b can be equalized. Thereby, an active material is consumed completely at an outlet of the fuel electrode in the cell group 1b so that mixed gas containing only the carbon dioxide and the water is exhausted. Furthermore, the carbon dioxide in combustion exhaust gas flowing in a conduit 108 is sucked up to the fuel electrode side from the air electrode sides 5a and 5b in the cell groups 1a and 1b. Thereby, the carbon dioxide can be recovered efficiently.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to thermal power plants and other power plants,
The present invention relates to a method of operating a molten carbonate fuel cell for separating and recovering carbon dioxide gas generated from a reformer or hydrogen production device using a natural gas reforming reaction.

[Conventional technology]

From the perspective of preserving the earth's environment, there is a need to regulate the release of carbon dioxide into the atmosphere, and several technical means for this purpose have been disclosed.

For example, Japanese Patent Application Laid-Open No. 63-21157 describes a method for separating and recovering carbon dioxide gas in a fuel cell power generation plant.
The phosphoric acid fuel cell power generation plant described in Publication No. 1, or Japanese Patent Application Laid-Open No. 519071, Japanese Patent Application Laid-open No. 1997-
Examples include those described in Publication No. 187775.

In the method described in JP-A No. 63-211571, hydrogen containing carbon dioxide gas is first introduced into the fuel electrode side of the fuel cell, the hydrogen is consumed by an electrochemical reaction, and a higher concentration is produced at the outlet of the cell. It begins by producing gas including carbon dioxide. This highly carbonated gas is then compressed and stripped to a carbon dioxide absorber (eg, a liquid absorbent such as monoethanolamine). This carbon dioxide-rich absorbent is depressurized and sent to a regeneration tower.
Further heating releases carbon dioxide gas, which is then cooled, compressed to the desired pressure, and pumped out of the system.

In the methods described in JP-A-519071 and JP-A-1-187775, the exhaust gas is removed by passing through a gas adsorption/separation device separately provided in the path.

Furthermore, other known examples include Arch, E, J.
Vol.

28103 shows an example of a report on a basic investigation into an attempt to remove carbon dioxide from the air inside a spacecraft using a molten carbonate fuel cell. This is done by supplying air with a low carbon dioxide concentration of 1% or less to the air electrode side of a molten carbonate fuel cell, causing the carbon dioxide contained in the air electrode side to move to the fuel electrode side through a chemical reaction in the cell. It is intended to remove carbon dioxide from gas.

[Problem to be solved by the invention]

Among the above-mentioned conventional techniques, the one described in JP-A-63-211571 only concentrates and separates carbon dioxide contained in hydrogen-containing fuel gas, and uses gas that does not contain hydrogen, such as general It cannot be used as a method for separating or recovering carbon dioxide gas from combustion exhaust gas, etc. In addition, new equipment and operations have been added in addition to conventional power generation plant equipment, such as absorption towers, regeneration towers, and associated compression, depressurization, heating, and cooling operations, making the system's equipment configuration complex and cost-effective. A problem exists.

Furthermore, it is impossible to obtain more carbon dioxide gas at the fuel electrode outlet than the amount of carbon dioxide gas entering the cell inlet, and the overall recovery efficiency cannot necessarily be said to be high.

Also, JP-A-51-9071, JP-A-1-187
The method described in Japanese Patent No. 775 also requires special equipment and piping systems for gas adsorption and separation, and also has the problem that the recovery efficiency and rate are not necessarily sufficient.

Furthermore, AICh, E, J, Vol, 28103
Although there is a disclosure of a technique for transferring carbon dioxide gas in the air electrode gas to the fuel electrode side using a molten carbonate fuel cell, there is no particular disclosure regarding the subsequent process. In other words, it is unclear how to treat the carbon dioxide gas generated on the fuel electrode side, and there is no specific description of how to operate a molten carbonate fuel cell (low carbon dioxide concentration on the air electrode side). 4) An object of the present invention is to provide a simple and highly efficient method for separating and recovering carbon dioxide gas in a target gas using a molten carbonate fuel cell.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a gas mainly composed of hydrogen, water, carbon dioxide, carbon monoxide, methane, etc.
Carbonate ion (CO32-) or oxygen ion (O
2-), an electrochemical reaction is carried out within the fuel electrode, and at the same time, the amount of current or the flow rate of the above gas is controlled to completely exhaust the active material of the electrochemical reaction, and the above gas is converted into carbon dioxide and water. The present invention discloses and provides a method for separating and recovering carbon dioxide gas, which is characterized in that a gas rich in carbon dioxide gas is obtained by changing the composition of the gas to a gas rich in carbon dioxide gas, and then removing water.

Furthermore, as a preferred embodiment of implementing the above method, a molten carbonate fuel cell is used, and a nonflammable gas containing carbon dioxide to be removed and air are allowed to flow into the air electrode side, and air is allowed to flow into the fuel electrode when necessary. By operating the fuel cell to generate a maximum current determined by the amount of active material flowing into the fuel cell, carbon dioxide gas in the air electrode is extracted as a mixture of carbon dioxide gas and water at the fuel electrode side outlet, and electric power is also generated. The present invention also provides a method for separating and recovering carbon dioxide, and an apparatus therefor.

Furthermore, as an aspect of using the above method as a power generation device,
The fuel cell group is divided into two, and the fuel gas supply section and discharge section on the fuel electrode side are divided into multiple systems corresponding to each, and one group (first cell group) is operated using the normal operation method. The other battery group (second battery group) is operated to generate a maximum current determined by the amount of active material flowing into the fuel electrode, and the carbon dioxide gas in the air electrode is transferred to the fuel electrode. A fuel cell power generation device is also disclosed which is capable of extracting a mixture of carbon dioxide gas and water at a side outlet and also supplying electric power.

Furthermore, when the total fuel utilization rate U is given as an operating condition for the two battery groups, the operation is such that the constant fuel flow rate x satisfies the relationship of the following equation (1). A fuel cell power generation device is also disclosed.

However, Z2: Total electrode area of the second battery group Zl: Total electrode area of the remaining battery groups The target gas for separating and recovering carbon dioxide gas is natural gas itself or hydrogen-containing gas obtained by reforming natural gas. Vine used.

[For production]

In a molten carbonate fuel cell, carbon dioxide gas on the air electrode side becomes an equivalent amount of carbonate ions through an electrochemical reaction and reacts with hydrogen at the fuel electrode, producing carbon dioxide gas C02 and water H2°. That is, on the fuel electrode side, not only is hydrogen consumed, but carbon dioxide and water are also produced in exactly equivalent amounts. In other words, a molten carbonate fuel cell plays the role of a separation membrane that selectively sucks up carbon dioxide from the air electrode side to the fuel electrode side.
On the fuel electrode side, hydrogen is consumed and carbon dioxide and water increase. Further, the material balance of these gases is controlled only by the amount of electrochemical reaction, that is, the amount of current flowing through the battery. In other words, by controlling the amount of current, the amount of hydrogen consumed, water, and carbon dioxide gas produced can be controlled.

The present invention applies this principle to actively recover carbon dioxide gas using a molten carbonate fuel cell.

Normally, in power plants using molten carbonate fuel cells, in order to improve the efficiency of the entire system, the maximum The operating point is not set at the current value, but at the current value where the amount of electric power is the largest. At this time, the fuel electrode outlet contains unreacted hydrogen, carbon dioxide, carbon monoxide, water,
In some cases, a mixture of gases such as methane comes out. Collecting and separating only carbon dioxide gas from such a mixed gas requires equipment such as an absorption tower and a regeneration tower in addition to the facilities necessary for power generation, as described in the description of the prior art.

In the present invention, operation is performed at a maximum current value that is larger than the normal operating point. As a result, the reaction active materials, hydrogen and carbon dioxide, are completely consumed, and a gas containing only carbon dioxide and water as products is discharged from the fuel electrode side outlet. Separation of carbon dioxide gas and water is relatively easy, and only carbon dioxide gas can be easily separated. Furthermore, since an electrochemical reaction is occurring at the same time, it has the effect of being able to supply electricity at the same time as separating carbon dioxide gas.

Further, hydrogen as an active material is also indispensable when carrying out the present invention. The ratio of the amount of hydrogen required to the amount of carbon dioxide gas recovered, that is, the efficiency, will be considered by taking as an example the case where hydrogen is generated from methane by a reforming reaction. When hydrogen is produced from methane by a reforming reaction, carbon dioxide gas is produced as a byproduct at a ratio of 1 mole of carbon dioxide per 4 moles of hydrogen. When this reformed gas is flowed to the fuel electrode side of a molten carbonate fuel cell, theoretically, 4 moles of hydrogen will be converted into 4 moles of carbon dioxide and 4 moles of water on the fuel electrode side due to the supply of carbonate ions from the air electrode. It is converted into moles, and 1 mole of carbon dioxide originally supplied from the maximum fuel outlet is added, and at the outlet, 5 moles of carbon dioxide and 4 moles of water are added.
When a mole is discharged, it becomes. Therefore, when water is separated,
This means that 5 moles of carbon dioxide gas can be separated and recovered. In addition, electric power can also be supplied by the electrochemical reaction of 4 moles of water, so the use of a molten carbonate fuel cell is considered to be an extremely efficient means of separating and recovering carbon dioxide gas.

With this method, in order to separate and recover carbon dioxide gas,
Since there is no need to use a larger amount of energy, there is no need for the contradiction of emitting more carbon dioxide into the atmosphere in order to recover it.

When the present invention is applied to a power generation plant using a molten carbonate fuel cell, depending on the mode of application, the power generation efficiency may be lowered due to operation at the maximum current value. Accordingly, in one embodiment of the present invention, the cell group is divided into two, and only the negative molten carbonate fuel cell is operated at maximum current. As described below, even in that case, the separation of carbon dioxide as a whole,
The recovery ability is outstanding.

For example, when using reformed methane gas, which is one of the fuels in a typical molten carbonate fuel cell, if the total fuel flow rate is 10 moles (hydrogen: 8 moles, carbon dioxide: 2 moles), then the Assuming that 10% of the fuel, that is, 0.8 mol of hydrogen and 0.2 mol of carbon dioxide, is supplied to the fuel electrode side of a molten carbonate fuel cell operating at maximum current, as explained earlier, If all the hydrogen in the fuel electrode of the cell is consumed, one mole of carbon dioxide gas, which is five times the amount of carbon dioxide gas at the inlet, will be exhausted at the outlet. This 1 mol of carbon dioxide is equivalent to 2 mol of carbon dioxide in the total fuel.

Even though the proportion of the total power generation of a molten carbonate fuel cell plant is 10% (in other words, it is 1/10 of the fuel ratio), the carbon dioxide gas separation and recovery capacity is limited to the carbon dioxide contained in the total fuel. This means that it corresponds to 50% of the amount. Of course, this relationship changes depending on the composition ratio of hydrogen and carbon dioxide in the fuel, and the greater the proportion of hydrogen in the fuel, the greater the effect of separating and recovering carbon dioxide.

Furthermore, as a specific method of dividing the batteries into the two groups mentioned above, Equation (1) is proposed, or by satisfying this relationship, no matter what load current flows through the two batteries connected in series. , the total fuel utilization rate U, and the fuel flow rate X are maintained, the load current value will always be the theoretical maximum current value for the battery group that separates and recovers carbon dioxide gas. become. If the relationship like equation (1) is not satisfied, in order to generate the maximum current value in the battery, the current values flowing through the two batteries must be different, and one It is difficult to control this in the power system.

In other words, due to the effect of equation (1), in the conventional case, the reactant gas supply flow rate per unit electrode area was the same for both cells, but in this case, the unit area is the same for all cells. Either the flow rate for the two divided battery groups is the same as before, or the flow rate of the reactant gas per unit area of the cell is no longer the same for each of the two divided battery groups. In other words, in a battery group for the purpose of carbon dioxide separation and recovery, according to equation (1), the flow rate per unit electrode area is always a constant ratio, that is, the total fuel utilization rate U is multiplied by the same amount as before. The flow rate of the reaction gas is equal to the theoretical consumption amount of the reaction gas determined from the load current. No reaction gas is discharged from this outlet on the fuel electrode side (fuel electrode side),
Only carbon dioxide and water are emitted.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. This is a power plant using molten carbonate fuel cells. Natural gas 100, which is a raw fuel supplied from a fuel supply source 23, is preheated in a fuel preheater lO, enters the reformer 2 in a high temperature state together with steam 101, and undergoes a reforming reaction to convert hydrocarbons in the natural gas. changes into hydrogen and carbon monoxide, which are active materials for the electrochemical reaction at the fuel electrode, and into carbon dioxide and water, which are inert gases.

This reformed gas 102 is used in molten carbonate fuel cells 1a and 1b.
is introduced into the fuel electrodes 3a and 3b. In addition, according to the operating specifications of this power generation plant, 80% of the reformed gas is always used for power generation in the fuel cell regardless of the power load, and the remaining 20% is used for the burner 4 in the reformer. and is used as a heat source for the above reforming reaction. That is, the fuel utilization rate U
, is always 0.8 for the power load.

The fuel cell is divided into two parts: a fuel supply system and an exhaust system for supplying fuel to the fuel electrodes 3a and 3b of each cell.

As a result, the fuel cells are divided into a fuel cell group 1a corresponding to one fuel supply system 103a and a fuel cell group 1b corresponding to the other fuel supply system 103b, or the electric power system This is the same as when there is only one fuel system. Note that the air electrode sides 5a and 5b have a conventional supply and exhaust system.

The structure of the above fuel cell will be explained in more detail with reference to FIG. If the proportion of fuel supplied to the fuel cell group 1b consisting of cells 30b among the reformed gas supplied to the fuel cell is always X regardless of the size of the fuel flow rate, then the fuel cell consisting of cells 30a The total fuel electrode area Z1 of the group 1a and the total fuel electrode area Z2 of the fuel cell group 1b are determined so as to satisfy the relationship of equation (1).

Note that the reformed gas is supplied to each supply header 31a.
, 31b, a conventional fuel cell or
When operating so that the same flow rate of gas is distributed to each cell as in the case of the air electrode side of the fuel cell in this example, formula (2) is used.
However, by maintaining the relationship of formula (1), each cell 30a, 30 of the fuel cell group 1a and fuel cell group 1b
The flow rate of the reformed gas 102 supplied to b is different from the value according to equation (2).

Moreover, not only the flow rates are different, but also the fuel cell group 1
b is always the fuel utilization rate or 1.0, that is, the consumption amount of water and carbon monoxide within the battery, which is theoretically uniquely determined with respect to the load current flowing through the fuel cell group 1b, and the fuel cell group 1b. It is operated so that the flow rates of water and carbon monoxide contained in the reformed gas supplied to the gas header 31 with the largest fuel port are equal to each other. As a result, inside the gas header 32b on the fuel electrode outlet side of the fuel cell group 1b, water and carbon monoxide are consumed by an electrochemical reaction, and a mixture of only carbon dioxide and water, which is a product of the reaction, is generated. or will be ejected.

The fuel cell groups 1a and lb are electrically connected in series, and as shown in the figure, the electric system 104 including the inverter 22 is one system, and the current value flowing through the fuel cell groups la and lb is always the same. becomes.

In FIG. 1, the flow rate of the reformed gas supplied to the fuel cell group 1b is adjusted to the ratio of X stated in the above equation (1) with respect to the amount of reformed gas supplied to the entire fuel cell. Therefore, a flow control valve 6 is provided in the fuel supply system 103b. As one embodiment of the operating method according to the present invention, the ratio of the amount of reformed gas supplied to the fuel cell 1b, that is, the value of X in equation (1), is controlled to 0.1. In this case, from equation (1), the total number of cells in the battery group 1b is 12.5% of the total number of cells in the battery groups 1a and 1b.

The present invention will be explained in detail with respect to the specific amount of carbon dioxide gas separated and recovered while keeping track of the balance of carbon dioxide gas in this power generation plant at this time.

For ease of explanation, the reformed gas 1 exiting the reformer 2
The composition of 02 is made to be only hydrogen and carbon dioxide gas, and the molar ratio thereof is 4:1. In reality, carbon monoxide and water are also included due to the shift reaction, and even if these are ignored, the effects of the present invention will not be affected. Regarding the amount of gas, for convenience, the amount of raw fuel supplied to this power plant is
It is set to 0. Assuming that the raw fuel is methane, it is assumed that 100 units of supplied methane is converted by the reformer 2 into 400 units of hydrogen and 100 units of carbon dioxide. This example is
This reformer 2 separates and recovers the carbon dioxide gas generated.

According to the above explanation, the battery group 1a has 360 units of hydrogen,
90 units of carbon dioxide gas are supplied to the fuel electrode 3a, while 40 units of hydrogen and IO units of carbon dioxide gas are also supplied to the fuel electrode 3b of the cell group 1b. From the fact that U is 0.8 and from equation (1), in the battery group 1a, 280 units out of 360 units of hydrogen are used in the electrochemical reaction and are consumed. As a result, 80 units of residual hydrogen and 280 units each of carbon dioxide and water are generated in the outlet discharge pipe 105a of the fuel electrode 3a of the battery group 1a. As a result, the amount of carbon dioxide gas at the fuel electrode outlet is 90+280=370 units.

On the other hand, in the battery group 1b, all 40 units of hydrogen are used in the electrochemical reaction, so the amount of carbon dioxide gas in the outlet pipe 105b of the fuel electrode 3b is the amount produced by the electrochemical reaction.
0 units, and the amount of carbon dioxide contained in the reformed gas supply system 103b at the cell inlet is 10 units, which is a total of 50 units. In addition, 40 units of water are produced by electrochemical reactions.

The fuel electrode exhaust gas flowing through the outlet exhaust pipe 105a of the battery 1a and the fuel electrode exhaust gas, which is a mixed gas of only carbon dioxide and water, flowing through the battery 1b outlet pipe 105b are not mixed with each other, and the fuel electrode exhaust gas flows through the fuel preheater 10, Gas/gas heat exchanger 1
1. The exhaust gas is cooled by passing through a gas cooler 12, and finally, moisture in the exhaust gas is removed by a steam-water separator 13. the result,
80 units of hydrogen and 370 units of carbon dioxide flow into the exhaust gas system 106a from the battery 1a, and only 50 units of carbon dioxide flows into the exhaust gas system 106b of the battery 1b (after this, it is compressed and liquefied). It is packed into cylinders as carbon dioxide gas and made into a marketable product, or transported as a source of carbon dioxide gas to artificial farms).

Next, the fuel electrode exhaust gas of the battery group 1a is preheated by the blower 14, the gas/gas heat exchanger 11, and the reformer 2.
The hydrogen is sent to the burner section 4, where 80 units of unburned hydrogen are combusted, and the generated heat is used for the methane reforming reaction. Combustion exhaust gas 107 (carbon dioxide gas 3
70 units, water 80 units) passes through air preheater 15 and enters mixer 16 via conduit 108.

Air compressed by the compressor 18 of the gas turbine 17 enters the mixer via a separator 19 and an air line 109. In addition, a part of the exhaust gas 113 (recirculated gas) on the air electrode side of the battery groups 1a, lb is also transferred to the conduit 1 by the separator 20.
10 and into the mixer 16 by means of a blower 21. The combustion exhaust gas, which is a mixture of the air and the air electrode exhaust gas, is supplied to the fuel cell groups 1a and lb through an oxidizer supply system 114.
a and 114b, respectively. The battery 1
There is no particular mechanism for adjusting the distribution of flow rates to the air electrodes a and 1b, and therefore the distribution is done according to the ratio of the number of cells in each battery group. As a result, 87.5% of the oxidant gas is supplied to the air electrode 5a of the battery 1a, and 12.5% to the air electrode 56 of the battery 16.

Therefore, the amount of carbon dioxide gas supplied to the air electrode 5a of the battery group 1a is 87.5% of the 370 units of carbon dioxide gas amount in the combustion exhaust gas flowing through the conduit 108, that is, approximately 324
It also adds 87.5% of the amount of carbon dioxide in the cathode recirculated exhaust gas flowing through the unit and the conduit 110. Similarly, in the battery 1b, 12.5% of the amount of carbon dioxide in the air electrode exhaust gas is added to 46 units of carbon dioxide contained in the remaining 12.5% of the combustion exhaust gas.

At the air electrode 5a of the battery group 1a, 280 units of carbon dioxide gas and oxygen are used for an electrochemical reaction;
At the air electrode 5b of b, 40 units of carbon dioxide gas and other oxygen are consumed. As a result, the amount of carbon dioxide gas in the air electrode outlet pipe 111a of the battery 1a is 324-280=44 units (not including the recirculated gas). In addition, the battery 1
In the air electrode outlet pipe 111b of b, the amount of carbon dioxide is 46-4
0 = 6 units (not including recirculated gas).

As a result, the recirculating gas, 44+ 6 =50 units of carbon dioxide gas, 80 units of water, and the remaining air from which oxygen has been consumed flow into the separator 20 . The composition of the recirculated gas is, of course, equal to that of a gas mixture of 50 units of carbon dioxide, 80 units of water, and the remaining air from which the enzymes have been consumed. The gas other than the recirculated gas flowing into the recirculation system 110 is supplied to the auxiliary combustor 21 through a conduit 112. Therefore, the amount of carbon dioxide contained in the gas in the conduit 112 is 50 units.

Exhaust gas leaving the auxiliary combustor 21 passes through a conduit 115, performs work in the gas turbine 18, passes through an exhaust heat recovery boiler 70, and is discharged from a chimney 71 into the atmosphere.

As a result, the carbon dioxide gas generated in the reformer 2 is transferred to the battery group 1.
a to the auxiliary combustor 21 through the air electrode outlet pipe 111a.
and that which is discharged from the fuel electrode 3b of the battery group 1b through the exhaust system 106b.
50 units of carbon dioxide were separated by the battery 1b.

That is, by supplying 1/10 of the reformed gas to the battery 1b, it is possible to separate and recover % of the carbon dioxide gas generated in the reformer. Moreover, there is no need for any new equipment to separate carbon dioxide gas, and the fuel cell 1a
By simply adjusting the fuel flow rate distribution of 1b and 1b, almost 100% concentration of carbon dioxide can be recovered, and the equipment and operating costs associated with carbon dioxide recovery can be significantly reduced.

Further, in this embodiment, the fuel cell group 1a accounts for 0.875 of the total electric energy, and the remaining 0.125 is accounted for by the fuel cell ib. Therefore, the fuel cell group 1b
Because the fuel cell always performs maximum current operation determined from the reactant gas flow rate at the inlet, it is undeniable that the power generation efficiency is lower than that of the cell 1a, and the effect on the power generation efficiency of the entire fuel cell is small. In other words, the energy loss associated with the separation and recovery of carbon dioxide gas can be reduced.

A second embodiment will be explained using FIG. 3. Similar to the first embodiment, this embodiment also shows means for recovering carbon dioxide gas generated when hydrogen is produced from natural gas using a reformer.

Natural gas 100 containing mainly methane is led to the reformer 2, and part of the gas converted into hydrogen, carbon dioxide, water, and carbon monoxide, and preferably carbon dioxide generated in the reformer, is removed. In order to recover it, 20% of it is introduced into the fuel electrode side 3 of the molten carbonate fuel cell 1 through the flow rate control valve 6. After using the remaining hydrogen-rich gas 102a, that is, after using it for combustion in the combustor 40 of the gas turbine, the exhaust gas 103 is adjusted to around 600°C, and while maintaining that temperature, the battery is heated. Supplied to the air electrode 5. If the oxygen concentration in the exhaust gas is lower than the carbon dioxide concentration η, air 104 is mixed in from the air supply source 43 to make the oxygen concentration higher than the carbon dioxide concentration.

In this embodiment, as in the first embodiment, if the gas composition in the reformed gas 102b is 400 units of hydrogen and 100 units of carbon dioxide, then the fuel electrode 3 has an amount of hydrogen of 80 units and an amount of carbon dioxide of 20 units. The unit is air electrode 5 (= means the amount of carbon dioxide gas is 80 units.

By connecting the battery to an electric load 50 through the inverter 22 and passing a current through it, carbon dioxide gas on the air electrode side 5 is consumed due to an electrochemical reaction within the electrode, and conversely, carbon dioxide on the fuel electrode side 3 is consumed by the electrochemical reaction within the electrode. Hydrogen is reduced, and carbon dioxide and water are produced. When the load current is equal to the maximum current value determined from the amount of active material containing hydrogen supplied to the fuel electrode 3, the air electrode 5
The carbon dioxide inside is completely consumed, and no carbon dioxide is discharged at the outlet; on the contrary, only carbon dioxide and water are discharged from the three outlets on the fuel electrode side. That is, an operation is performed that consumes all the hydrogen in the fuel electrode and the carbon dioxide in the air electrode. The carbon dioxide gas and water, which are the exhaust gases on the fuel electrode side, are cooled by the cooler 12, and the water is removed by the steam-water separator 13, so that only the carbon dioxide gas can be taken out.

As a result, all of the carbon dioxide gas emitted as a byproduct during the operation of the reformer 2 (or the hydrogen production device) can be recovered, and the reformed gas introduced into the fuel cell used for recovery can be used to supply electricity. Separation and concentration of carbon dioxide gas 2
Since it performs two functions, there is no waste, and the reformer combined with the molten carbonate fuel cell can be operated efficiently.

In addition, if it is necessary to adjust the flow rate by the fuel flow valve 6 so that the load current is always equal to the maximum current of the battery, the hydrogen concentration at the fuel electrode outlet pipe 105 is constantly monitored by the detector 41. A method is used in which the flow control valve is controlled by the computing unit 42 so that the detected value becomes zero.

The third embodiment relates to a thermal power plant using natural gas, and will be explained using FIG. 4.

Here, a part of the fuel exhaust gas in the thermal combined power generation plant 73, for example, the exhaust gas containing carbon dioxide at the outlet of the gas turbine 74, is supplied to the air electrode side 5 of the molten carbonate fuel cell 1 via the flow valve 7. ing. In this case, it is desirable that the gas temperature is at least 600°C or higher. The fuel electrode 3 of the fuel cell 1 is equipped with a reforming catalyst 6. A portion of the natural gas 100 from the methane supply source 9 of the power generation plant is transferred to the fuel electrode 3 with water vapor 1
01 through the conduit 102 using the flow control valve 8.

The supply of natural gas flowing through the conduit 102 is adjusted so that the load current of the electrical load connected to the fuel cell is equal to the maximum current value of the cell.

The natural gas that has entered the fuel electrode 3 is converted into hydrogen by the reforming catalyst 6, and the hydrogen is consumed through an electrochemical reaction. As a result, neither natural gas nor hydrogen is discharged from the fuel electrode outlet side pipe 103, but carbon dioxide and water are discharged. On the other hand, the exhaust gas from the air electrode 5 has a temperature of 60% within the outlet pipe 105.
Since the temperature is as high as 0°C or higher, it is returned to the piping system 104 connected to the exhaust heat recovery plant 75.

According to this embodiment, even in a power generation plant without hydrogen, by using a molten carbonate fuel cell, carbon dioxide gas generated within the plant can be efficiently separated and recovered.

A fourth embodiment will be described using FIG. 5.

In this embodiment, a power generation plant consisting of two battery groups using the molten carbonate fuel cell shown in the first embodiment, that is, cells 30a are stacked, a fuel supply header 31a,
In addition to the battery group 1b consisting of the fuel supply header 31b and the discharge header 32b, the cell 30c is stacked. T layer, fuel supply header 31c
, and a battery group 1c consisting of the discharge header 32c.

The battery group 1a corresponds to the battery group 1a mainly used for power generation, which covers most of the power generation amount explained in the first embodiment, and its electrode layer area is the same as that of the first embodiment. The battery nTI
b and IC are connected to the carbon dioxide gas separation and recovery battery group 1b in the first embodiment, and the corresponding ? [Pond R1I b
Ic(')7ri, the total area is equal to the total electrode area of the battery 11lb of the first embodiment. That is, the fuel cell group for separating and recovering carbon dioxide gas was divided into two. In addition, electrically the 7IT, pond group 1a, l h, I
C are connected in series.

As described in the first embodiment, the reformed gas 102 is distributed to the fuel system 102 or 102, depending on the fuel distribution ratio determined by the required amount of carbon dioxide recovery, by the flow control valve 6.
3b to the fuel supply header 31b of the battery group 1b.
The electrochemical reaction occurs within the cell 3Ob and is led to the outlet header 32b. The header 32b
Based on the relationship between the electrode area of the battery group 1b, the fuel flow rate supplied to the fuel supply header 31b, and the load current, it is possible to determine whether unreacted hydrogen remains in the exhaust gas within the cell group 1b.
Its hydrogen concentration is low, and most of it is carbon dioxide and water, which are reaction product gases. This unreacted gas containing low concentration hydrogen is sent to the carbon dioxide absorption tower 6 () through the conduit 105t+.
The reactor reacts with water and carbon dioxide in the unreacted gas, and changes into calcium hydroxide Ca (O11) and calsilyl carbonate (CaCOt), respectively. This reaction is 5
(l D = 60 (Since the process is most active at a high temperature of 1°C, considering that the exhaust gas temperature of the battery 1b is 600°C or higher, the thermal problem is solved.

As a result, carbon dioxide in the unreacted gas in the absorption tower 60,
Conduit 1 leaving the absorption tower 60 where water is to be removed
The hydrogen concentration in the gas in 03C is high. This unreacted gas with increased hydrogen concentration is sent to the fuel supply header 31c of the cell group 1c, and an operation is performed in which the maximum current flows in the cell 30c. To the exit discharge - 3
At 2c, a mixed gas consisting only of carbon dioxide and water is discharged.

The exhaust gas passes through the preheater 10 and is cooled as shown in Example 1 above, and finally only carbon dioxide gas is recovered by steam/water separation.

In this way, by increasing the hydrogen concentration in the fuel gas, the deterioration in the performance of the cell group IC can be minimized as much as possible, and the efficiency of the entire power plant can be further increased than in Example 1. can. Regarding the position of the absorption tower 60, in order to absorb carbon dioxide gas in the fuel, the position of this embodiment allows the amount of gas flowing into the absorption tower to be relatively small compared to other positions of the power generation blunt. Moreover, since the concentration of carbon dioxide gas is high, a very small and compact absorption tower can be used. Fuel system 1 (
], 3b is also possible -C, but the carbon dioxide concentration is low. ?
With JYE, the equipment cost can be reduced compared to the case where an absorption tower or separator is installed at another location and carbon dioxide gas is separated and recovered as in this embodiment.

3. The final electrode area ratio between the battery groups 1b and Ic is not limited to a certain value, but may be set to an optimal ratio according to the capacity of the absorption tower 60 and the battery operating conditions. Also absorption tower 6
After the reaction of 0, calcium hydroxide and calcium carbonate can be reduced to Can again by heating. For example, calcium carbonate requires heating to 1000°C or higher, or calcium hydroxide requires heating to 580°C.
will be fully refunded.

Therefore, by performing the CaO regeneration process in the absorption tower using the high heat source in the power generation furnace, the CaO
This enables semi-permanent use of carbon dioxide, and enables efficient separation and recovery of carbon dioxide in combination with fuel cells.

〔Effect of the invention〕

According to the present invention, since a molten carbonate fuel cell is used to separate and recover carbon dioxide gas, carbon dioxide gas with a concentration close to 100% can be recovered without using any other equipment or equipment. The accompanying equipment and operating costs can be significantly reduced.

Furthermore, since electricity can be supplied while recovering carbon dioxide gas, energy loss associated with separation and recovery of carbon dioxide gas can be reduced, resulting in higher efficiency.

Furthermore, since it can be applied to plants that use natural gas even without hydrogen, it has the effect of further expanding the range of applications.

In those equipped with an absorption tower that reacts with carbon dioxide and water and adsorbs them, it is possible to improve the performance of the fuel cell due to the separation and recovery of carbon dioxide, which has the effect of further increasing power generation efficiency. .

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a power generation plant that is an embodiment of a carbon dioxide gas separation and recovery device using a molten carbonate fuel cell according to the present invention, and FIG. 2 shows the configuration of the fuel cell main body of FIG. 1. The schematic diagrams, FIGS. 3 and 4 respectively represent the second embodiment of the present invention.
, a plant system diagram showing the third embodiment, and FIG. 5 is a schematic diagram of the structure of the fuel cell main body and its vicinity, which is the fourth embodiment. la, lb... fuel cell, 2... reformer, 3a, 3
b...Fuel electrode, 5a, 5b...Air electrode, 6...Fuel flow rate control valve, 13...Steam water separator, 22...Inverter, 31a, 31b...Fuel supply header, 3
2a, 32b... Outlet gas header. Applicant Hitachi, Ltd. Representative Patent Attorney Yusuke Hiraki' Patent Attorney Satoshi Ishii Figure 105b 32b Figure 4

Claims (1)

[Claims] 1. Carbonate ions (CO_3^2^-),
Alternatively, an electrochemical reaction is performed with oxygen ions (O^2^-) in the fuel electrode, and at the same time, the amount of current or the flow rate of the gas is controlled to completely consume the active material of the electrochemical reaction. A method for separating and recovering carbon dioxide gas, which comprises changing the composition of gas into a gas rich in carbon dioxide gas and water, and then removing water to obtain a gas rich in carbon dioxide gas. 2. Using a molten carbonate fuel cell, inject nonflammable gas containing carbon dioxide to be removed and air if necessary into the air electrode side, and generate a maximum current determined by the amount of active material flowing into the fuel electrode. By operating the fuel cell in this manner, the carbon dioxide gas in the air electrode can be taken out as a mixture of carbon dioxide gas and water at the fuel electrode side outlet, and electric power can also be supplied. , collection method. 3. In a power generation device using a molten carbonate fuel cell,
The fuel cell group is divided into two, and the fuel gas supply section and discharge section on the fuel electrode side are divided into multiple systems corresponding to each, and one group (first cell group) is operated using the normal operation method. The other battery group (second battery group) is operated to generate a maximum current determined by the amount of active material flowing into the fuel electrode, and the carbon dioxide gas in the air electrode is transferred to the fuel electrode. 3. A fuel cell power generation device for carrying out the method according to claim 2, characterized in that the mixture of carbon dioxide gas and water can be taken out at the side outlet and can also be used to supply electric power. 4. In a power generation device using a molten carbonate fuel cell,
Divide the fuel cell group into two or more while keeping them electrically connected in series,
A fuel gas supply section and a discharge section on the fuel electrode side are divided into a plurality of systems corresponding to each one, and a flow rate adjustment section for adjusting the flow rate distribution of fuel to each is provided on the fuel supply side, At least one battery group (second battery group) always maintains a certain fuel flow rate ratio, regardless of the total amount of fuel supplied, depending on the ratio of its total electrode area to the total electrode area of all battery groups. 3. The method according to claim 2, wherein the flow rate adjusting section is operated to generate a maximum current determined from the amount of active material flowing into the fuel electrode in the battery group. Fuel cell power generation equipment for. 5. The fuel cell power generation device according to claim 4, wherein the constant fuel flow rate ratio x is expressed by the following equation (1). x=U_F・Z_2/Z_1+Z_2... (1) However, Z_2; Total electrode area of the second battery group Z_1; Total electrode area of the remaining battery groups U_F; Fuel utilization rate (fuel supplied to the entire battery) 6. A method for separating and recovering carbon dioxide gas generated when producing hydrogen by reforming natural gas, which is generated from a reformer. A portion of the gas is supplied to the fuel electrode side of the molten carbonate fuel cell, and after the active gas component has been used, air is mixed into the exhaust gas containing carbon dioxide gas as necessary, and then the air is supplied to the air electrode of the cell. 3. The method for separating and recovering carbon dioxide gas according to claim 2, wherein the carbon dioxide gas is supplied. 7. In a thermal power generation plant that uses natural gas, after bypassing some or all of the high-temperature exhaust gas containing carbon dioxide and adjusting the gas temperature to a specified temperature, it is necessary for the air electrode side of the attached molten carbonate fuel cell. A certain amount of air is mixed and flowed, and a portion of natural gas is supplied to the fuel electrode in the required amount, and hydrogen is generated by the reforming catalyst provided inside the fuel electrode.
By operating the fuel cell to generate the maximum current determined by the amount of active material, carbon dioxide gas in the air electrode can be extracted as a mixture of carbon dioxide gas and water at the fuel electrode side outlet, and electricity can also be supplied. A power generation plant that separates and recovers the carbon dioxide gas generated in the power generation plant. 8. The fuel cell power generation device according to claim 4, wherein the second
The fuel cell group in the battery group is divided into a plurality of cells, and further includes carbon dioxide adsorption means, which allows exhaust gas from the fuel electrode outlet of the upstream cell group to pass through the carbon dioxide absorbent. A fuel cell power generation device characterized in that the fuel cell power generation device absorbs carbon dioxide gas and moisture, increases the partial pressure of hydrogen, and then supplies the hydrogen to the fuel electrode of a downstream cell group. 9. The fuel cell power generation device according to claim 8, wherein the carbon dioxide absorbent is calcium oxide.