JP2011113726A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which a desulfurizer life can be directly and objectively determined as compared with a conventional technology. <P>SOLUTION: A single chamber type solid electrolyte fuel cell 5 is incorporated in a gas passage 11 between a desulfurizer 4 and a reformer 6. Air from an water/air supply part 10 can be mixed at a position at an upstream side of the single chamber type solid electrolyte fuel cell 5 and a downstream side of the desulfurizer 4. By a controller 13, air from the water/air supply part 10 is intermittently mixed for each predetermined detection timing, and a gaseous mixture of the air and a raw material gas is supplied to detect a power generation output by the single chamber type solid electrolyte fuel cell 5. When the power generation output falls below a predetermined level, it is determined that a sulfur content flows out, i.e., the desulfurizer 4 comes to the end of life thereof, and the determination result is informed by an informing means 13a. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell system in which a sulfur content (sulfur compound) in a fuel gas is removed by a desulfurizer and reformed, and the reformed gas is supplied to a fuel cell to generate electric power. This relates to a technology that can easily determine the above.

  In a fuel cell system, in order to prevent a catalyst, an electrode, and the like from being poisoned by a sulfur content in a raw material gas, a reforming process is performed after the sulfur content is removed by a desulfurizer. That is, as illustrated in FIG. 4, a hydrocarbon-based gas is introduced as a raw material gas, and the sulfur content contained is adsorbed and removed by passing the raw material gas through a desulfurizer 400, and the raw material gas after the removal of the sulfur content is removed. For example, steam reforming is performed in the reformer 600 by mixing steam, and the hydrogen-rich fuel gas after reforming is supplied to a fuel cell 700 (in the example, a solid oxide fuel cell: SOFC is illustrated) 700 for power generation. To do. In such a process, if the adsorption removal capability of the desulfurizer 400 is saturated, it is necessary to replace the desulfurizer 400. Conventionally, the life of the desulfurizer 400 is determined and detected in order to grasp the replacement timing and the like. Techniques for this have been proposed.

  For example, Patent Document 1 proposes a desulfurization agent for adsorbing and removing a sulfur content, which has an indicator function capable of displaying the lifetime of the adsorption capacity by changing the hue. And it is disclosed that the life of the desulfurizer can be detected by filling the desulfurizer with the indicator function in the desulfurizer and observing and visually checking the hue change.

  Patent Document 2 proposes a technique for optically determining the color change state of the desulfurizing agent. That is, the light projecting means projects light onto the desulfurizing agent in the desulfurizer, the light emitted from the light receiving means is received, and the color change state of the desulfurizing agent is determined based on the light receiving state. The life of the desulfurizing agent is determined based on the above.

  In Patent Document 3, a single-chamber solid electrolyte fuel cell is proposed as a fuel cell that can be reduced in cost with a simple structure. This is proposed as a solution that can eliminate the complexity and cost increase of conventional fuel cells, which were a two-chamber system in which fuel gas was supplied to the fuel electrode and air was supplied separately to the air electrode. ing.

Japanese Patent Laid-Open No. 2002-358992 JP 2008-128957 A Japanese Unexamined Patent Publication No. 2000-243412

  However, as disclosed in Patent Document 1, as a technique for judging the life of the desulfurizer, the method of observing the hue change of the desulfurizing agent is not objective and easily causes variations, and realizes automatic processing. I can't do it.

  Further, as disclosed in Patent Document 2, the method for determining the discoloration state of the desulfurizing agent based on the light receiving state of the light emitted from the desulfurizing agent lacks objectivity as described above, and the determination result is indirect. Tend to be too specific.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel cell system capable of determining the life of a desulfurizer more directly and objectively than in the prior art. Is to provide.

  In order to achieve the above object, the first invention comprises a desulfurization means for removing the sulfur content in the fuel gas, and a reformer for reforming the fuel gas from which the sulfur content has been removed by the desulfurization means. The following specific items are provided for a fuel cell system that performs a power generation operation using the fuel gas reformed by the reformer. That is, an air supply unit that supplies and mixes air to the gas flow path connecting the desulfurization means and the reformer, and a downstream side of the position where the air from the air supply unit is mixed and the reforming The single chamber type solid oxide fuel cell interposed in the gas flow path at the upstream position of the vessel and the air supply unit mix air and detect the power generation output of the single chamber type solid oxide fuel cell. Accordingly, it is provided with life determination control means for performing the life determination processing of the desulfurization means (claim 1).

  In the fuel cell system of the present invention, the life determination control means intermittently mixes the air from the air supply unit, and intermittently detects the power generation output of the single-chamber solid electrolyte fuel cell. (Claim 2).

  In the second invention, a desulfurization means for removing the sulfur content in the fuel gas and a reformer for reforming the fuel gas from which the sulfur content has been removed by the desulfurization means are provided. The following specific items are provided for a fuel cell system that performs a power generation operation using the generated fuel gas. That is, a branch gas flow path that branches from the middle of the gas flow path connecting the desulfurization means and the reformer, a single chamber type solid electrolyte fuel cell interposed in the branch gas flow path, and the single chamber An air supply unit for supplying and mixing air to the upstream position of the solid electrolyte fuel cell, and detecting the power generation output of the single-chamber solid oxide fuel cell by mixing air with the air supply unit Thus, it is provided with life determination control means for performing the life determination processing of the desulfurization means (claim 3).

  In the case of the above first or second invention, a single-chamber solid electrolyte fuel cell (hereinafter referred to as “single-chamber SOFC”) is used as a sulfur content detection sensor for detecting sulfur content, and a single-chamber SOFC is used. It is possible to detect the decrease in the power generation output as the outflow of the sulfur content from the desulfurization means. In other words, a single-chamber SOFC has a fuel electrode and an air electrode arranged in the same space, and can generate power when a mixture of fuel gas and air is supplied, while the supplied fuel gas contains sulfur. If this occurs, the sulfur material will poison the electrode material and cause a decrease in power generation output. Therefore, by mixing the air from the air supply unit at the sulfur content detection timing and detecting the power generation output of the single-chamber SOFC, the sulfur content flows out from the desulfurization means in an undesulfurized state, that is, the desulfurization means. It is possible to determine that the desulfurization ability is reduced and the life is reached. In other words, if the detected power generation output is lower than the set value, it can be determined that the lifetime is reached. Thereby, it is possible to objectively determine the lifetime of the desulfurization means by directly detecting the outflow of the sulfur content. In the first aspect of the invention, the life can be determined intermittently at a predetermined timing. In the second aspect of the invention, a single-chamber SOFC is used separately from the power generation by the original fuel cell. It is also possible to continue the life determination and always perform it.

  In the first or second aspect of the invention, a notification unit is provided, and when the power generation output of the single-chamber fixed electrolyte fuel cell is equal to or less than a predetermined set value as the lifetime determination control unit, the notification is performed. By this means, the desulfurization means can be configured to notify that the life or replacement time has been reached (Claim 4). By doing so, it is possible to reliably notify the user that the desulfurization means has reached the end of its life and the replacement time.

  As described above, according to the fuel cell system of the present invention, the single chamber type SOFC can be used as a sulfur content detection sensor for detecting the sulfur content, and detection of a decrease in the power generation output of the single chamber type SOFC is detected. Can be detected as the outflow of sulfur from the desulfurization means. That is, by detecting the power generation output of the single-chamber SOFC by mixing air from the air supply unit at the sulfur content detection timing, the sulfur content flows out from the desulfurization means, that is, the desulfurization ability of the desulfurization means is reduced. Thus, it can be determined that the lifetime has been reached. As a result, it is possible to objectively determine the life of the desulfurization means by directly detecting the outflow of the sulfur content.

  In particular, according to claim 2, the life determination can be performed intermittently at a predetermined timing, and according to claim 3, the life determination using the single-chamber SOFC is continued separately from the power generation by the original fuel cell. Can be done at any time.

It is a mimetic diagram showing a 1st embodiment of the present invention. It is explanatory drawing which shows the example of a single chamber type solid electrolyte fuel cell. It is a schematic diagram which shows 2nd Embodiment. It is a schematic diagram which shows a prior art example in order to demonstrate the conventional subject.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 shows a fuel cell system according to a first embodiment of the present invention. This fuel cell system desulfurizes sulfur from a hydrocarbon-based source gas (for example, city gas), reforms the source gas after desulfurization into a hydrogen-rich fuel gas by steam reforming, and uses this fuel gas. Electricity is generated by a fuel cell. In particular, when city gas is used as the raw material gas, the sulfur content is contained in the odorant in the city gas, and it is necessary to remove this sulfur content. The characteristic component of this fuel cell system is that the life of the desulfurizer 4 as a desulfurization means installed for desulfurization of sulfur content (more precisely, the life of the desulfurization agent filled in the desulfurizer) is obtained. In order to make the determination and detection more directly and objectively, a single-chamber solid electrolyte fuel cell (hereinafter referred to as “single-chamber SOFC”) 5 is used as a sulfur content detection sensor. The sulfur content in the raw material gas after desulfurization is detected. Details will be described below.

  A pressure pump 2, a flow sensor 3, a desulfurizer 4, a single chamber SOFC 5, a reformer 6, a fuel cell (solid oxide fuel cell; SOFC) are connected to the gas flow path from the gas inlet 1 through which the raw material gas is introduced. Exemplification) 7, an off-gas combustion unit 8 and an exhaust heat recovery heat exchanger 9 are mainly interposed. The raw material gas (for example, city gas) introduced from the gas inlet 1 is boosted by the booster pump 2 and then passed through the desulfurizer 4 through the flow rate detection by the flow rate sensor 3. The desulfurizer 4 is filled with a desulfurizing agent, and the sulfur content contained in the raw material gas is adsorbed and removed (desulfurized) by contacting with the desulfurizing agent. If the desulfurization agent adsorbs a predetermined amount of sulfur and reaches saturation, that is, if the desulfurization agent reaches the end of its life, no further sulfur will be adsorbed and flowed downstream without being adsorbed. Become. When the desulfurization agent reaches the end of its life, the adsorption capacity of sulfur is not instantaneously reduced to zero, but when it approaches saturation, the adsorption capacity that had been exhibited well until then begins to gradually decrease. It has a characteristic that it reaches a saturated state (a state where the adsorption capacity is zero) over several hours. In consideration of such characteristics, an intermittent detection timing for sulfur detection is set as described later. Therefore, at the normal timing when sulfur detection is not performed, the raw material gas after desulfurization passes through the single-chamber SOFC 5 and is introduced into the reformer 6. In the gas flow path of the desulfurizer 4 to the single-chamber SOFC5 to the reformer 6, a water / air supply unit provided with a blower or the like on the upstream gas flow path before being introduced into the single-chamber SOFC5 10 can supply air from the water / air supply unit 10 to the gas flow path between the single-chamber SOFC 5 and the reformer 6. It has become. The water / air supply unit 10 described above constitutes an air supply unit.

  The single-chamber SOFC 5 can generate electric power even if a fuel electrode and an air electrode are installed in the same space, and an example of the structure is shown in FIG. That is, a fuel electrode 52 and an air electrode 53 formed of a Ni-based material are attached to the solid electrolyte 51, and this single chamber type SOFC 5 is disposed in the gas flow path 11 through which the raw gas after desulfurization flows. It is arranged. In the single-chamber SOFC 5, no electromotive force is generated when only the source gas flows in the gas flow path 11, and air is mixed from the water / air supply unit 10, so that the source gas and the air When the air-fuel mixture is supplied to the single-chamber SOFC 5, an electromotive force is generated. Therefore, if the raw gas after desulfurization is supplied from the desulfurizer 4 to the single chamber SOFC 5 without being supplied with air from the water / air supply unit 10, the single chamber SOFC 5 passes through the reformer 6. Will be introduced.

  The operation principle that can utilize such a single chamber type SOFC5 as a sulfur content detection sensor is as follows. That is, if the desulfurization agent of the desulfurizer 4 is close to saturation and the sulfur content begins to flow out into the raw material gas, the sulfur content adheres to Ni which is the material of the fuel electrode of the single-chamber SOFC 5 and Ni is You will be poisoned. Since the electromotive force and output voltage of the single-chamber SOFC 5 decrease due to this poisoning, the sulfur content is detected by detecting the decrease in the output voltage, thereby determining the life of the desulfurizer 4. Will get. Note that air is mixed into the gas flow path for sulfur content detection, but oxygen in the air is combined with carbon in the raw material gas to become CO or CO 2, so that the fuel electrode of the fuel cell 7 There is no inconvenience. Details of the life determination method using the single-chamber SOFC 5 will be described later.

  The reformer 6 performs steam reforming of the raw material gas using the steam supplied from the water / air supply unit 10, and supplies the reformed hydrogen-rich fuel gas to the fuel electrode of the fuel cell 7. ing. The reformer 6 and the single-chamber SOFC 5 are accommodated in the same compartment 12, and the combustion heat described later is supplied to the compartment 12 to heat the single-chamber SOFC 5 together with the reformer 6. ing. As a result, the temperature is raised to the temperature for the power generation operation (measurement for sulfur content detection) of the single-chamber SOFC 5, and the heater for power generation operation can be omitted. That is, by installing the single-chamber SOFC 5 in the same installation space as the reformer 6, the heater for raising the temperature up to the temperature required for the power generation operation for measuring the single-chamber SOFC 5 is omitted. In addition to installing the single-chamber SOFC 5 in the same compartment 12 as described above, the single-chamber SOFC 5 is disposed in contact with the reformer 6, for example, so as to omit the above-described temperature raising heater. Also good.

  The fuel battery cell 7 includes a fuel electrode and an air electrode formed of ceramics containing a metal oxide such as Ni, and is formed of a solid oxide such as YSZ (yttrium stabilized zirconia) as an electrolyte. . In the fuel cell 7, cathode air is supplied to the air electrode from a blower of an air supply unit (not shown), oxygen in the cathode air passes through the electrolyte as oxygen ions, and hydrogen in the fuel gas is While reacting to generate water (water vapor), the generated electrons are repeatedly generated by moving to the air electrode side through the circuit and ionizing oxygen again. After the fuel gas supplied to the fuel electrode is used for the above reaction, unused hydrogen-rich off-gas is guided to the off-gas combustion unit 8 and used as a fuel for combustion, and this combustion heat is supplied to the reformer 6. It is supposed to be sent. Then, the exhaust gas from the off-gas combustion unit 8 is sent to the exhaust heat recovery heat exchanger 9, and the recovered heat is sent to heat the air and water of the water / air supply unit 10, for example, while the exhaust heat recovery Exhaust gas is discharged.

  The above-described operation for power generation by the fuel cell system, processing control for determining the life of the desulfurizer 4, and the like are controlled by the controller 13 including a life determination control means. Hereinafter, the life determination process when the single-chamber SOFC 5 is used as a sulfur content detection sensor by the life determination control means of the controller 13 will be described.

  A specific example of the life determination process is as follows. In other words, the timing of the start of measurement (start of detection operation) may be from the initial state of the desulfurizer 4 (initial state of the desulfurizing agent), but is preferably started after a lapse of a predetermined time from the start of operation. That's fine. For example, the measurement (detection) may be started after the elapse of a predetermined time when it is expected that the adsorptive desulfurization ability of the desulfurizing agent will start to decrease after the operation starts. As such a predetermined time value, a test value obtained by testing the relationship between the supply amount of the raw material gas and the adsorptive desulfurization ability and filling amount of the desulfurizing agent, or a value on the safe side from the experience values may be adopted. The measurement timing after the start of measurement (detection operation interval) may be intermittent measurement (intermittent detection) that is performed every elapse of a predetermined time (for example, 1 hour or 2 hours). This is because the above-described characteristics of the desulfurization agent up to the saturation state of the adsorption desulfurization ability are taken into account, and it is sufficient if it is possible to detect and determine that the saturation, that is, the lifetime is near, immediately before reaching the saturation state. It is. In addition to such intermittent measurement, the occurrence of fluctuations in the output voltage on the fuel cell 7 side, for example, is monitored. Measurement (detection) for detection of sulfur content by means of may be performed. That is, the measurement timing may be added based on the situation on the fuel cell 7 side.

Next, the life criteria may be as follows. First, the power generation output (initial voltage) in the initial state of the desulfurizing agent is detected and stored, and the detected value of the power generation output (output voltage) at the above measurement timing is set to a set value (for example, 5%) from the initial voltage. If it is lower than the reduction value), the desulfurizing agent is in the immediate vicinity of reaching saturation, and the sulfur content is leaking downstream of the desulfurizer 4, that is, it has reached the end of its life and needs to be replaced. To do. Alternatively, if the detected output voltage tends to decrease continuously three or more times, the life may be determined to be safe. The above set value may be set from the viewpoint of what level of sulfur content leaks into the raw material gas, and for example, a sulfur content of several ppm (mainly present as H ₂ S) in the fuel gas. ), The OCV (no-load voltage) is reduced by about 10 to 20% and the power generation efficiency is lowered. Therefore, the output is reduced by 5% or more from the initial voltage or the output voltage detected last time. If this is the case, the desulfurizer 4 may be determined to have a lifetime. When it is determined that the service life is reached, a notification control signal is output to the notification means 13a, and the notification means 13a notifies that the desulfurizer 4 is at the end of its life and needs to be replaced. As the notification, for example, display by a display unit, notification by voice guidance, lighting of a warning lamp, or the like may be performed.

  According to the lifetime determination process described above, the presence of sulfur can be directly detected, and the lifetime can be objectively determined based on the electrical output value. Moreover, such a life determination can be easily realized simply by installing the single chamber SOFC 5 in the gas flow path 11.

Second Embodiment
FIG. 3 shows a fuel cell system according to the second embodiment of the present invention. The second embodiment relates to a system that makes it possible to always determine the life of the desulfurizer. In addition, about the component similar to 1st Embodiment, the same code | symbol as 1st Embodiment is attached | subjected and the detailed description which overlapped is abbreviate | omitted.

  In the second embodiment, the gas flow path 11 is branched at a downstream position of the desulfurizer 4, and the single-chamber SOFC 5 is interposed in the branch gas flow path 11a. The original gas flow path 11 is connected to the reformer 6 as it is.

  A small amount of source gas is diverted from the gas channel 11 through the restrictor 11b to the branch gas channel 11a, and air is supplied from the water / air supply unit 10 to the small amount of source gas. Is to be supplied. The amount of the small amount of source gas to be branched may be set to the minimum flow rate value necessary for detecting the sulfur content in the single chamber SOFC 5. Then, a mixture of raw material gas and air is always supplied to the single-chamber SOFC 5, and the power generation operation is always performed in the single-chamber SOFC 5 by the constantly supplied mixture, and the above-described life determination process is always executed. Will be. The exhaust gas after power generation is joined to the off gas outlet from the fuel cell 7 through the exhaust gas passage 11c and used for off gas combustion and exhaust heat recovery.

  Also in the case of the second embodiment, the single-chamber SOFC 5 is housed in the same compartment 12 together with the reformer 6, receives supply of combustion heat from the off-gas combustion section 8, and the single-chamber SOFC 5 Omission of heaters and the like for power generation operation is attempted. The supply / mixing of air from the water / air supply unit 10 may be performed on the gas flow path 11 upstream of the branch gas flow path 11a.

4 Desulfurizer (desulfurization means)
5 Single-chamber SOFC (single-chamber solid electrolyte fuel cell)
6 Reformer 7 Fuel cell 10 Water / air supply part (air supply part)
13 Controller (Life judgment control means)
13a Notification means

Claims (4)

A desulfurization means for removing sulfur content in the fuel gas and a reformer for reforming the fuel gas from which sulfur content has been removed by the desulfurization means are provided, and power generation operation is performed by the fuel gas reformed by the reformer. A fuel cell system to perform,
An air supply unit that supplies and mixes air to a gas flow path connecting the desulfurization means and the reformer, and a downstream side of a position where the air from the air supply unit is mixed and the reformer By detecting the power generation output of the single-chamber solid electrolyte fuel cell by mixing air by the single-chamber solid electrolyte fuel cell interposed in the gas flow path at the upstream position and the air supply unit A fuel cell system comprising a life determination control means for performing a life determination process of the desulfurization means. The fuel cell system according to claim 1,
The life determination control means is configured to intermittently mix the air from the air supply unit and to intermittently detect the power generation output of the single-chamber solid electrolyte fuel cell. . A desulfurization means for removing sulfur content in the fuel gas and a reformer for reforming the fuel gas from which sulfur content has been removed by the desulfurization means are provided, and power generation operation is performed by the fuel gas reformed by the reformer. A fuel cell system to perform,
A branch gas passage branching from the middle of the gas passage connecting the desulfurization means and the reformer, a single chamber solid electrolyte fuel cell interposed in the branch gas passage, and the single chamber solid An air supply unit that supplies and mixes air to the upstream side of the electrolyte fuel cell, and the desulfurization is performed by mixing the air with the air supply unit and detecting the power generation output of the single-chamber solid electrolyte fuel cell. A fuel cell system comprising: life determination control means for performing a life determination process of the means. The fuel cell system according to any one of claims 1 to 3,
Providing a notification means,
The life determination control means informs that the desulfurization means has reached the life or replacement time by the notification means when the power generation output of the single-chamber fixed electrolyte fuel cell becomes equal to or less than a predetermined set value. A fuel cell system configured as described above.

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