JPH0689347B2 - Fuel reforming system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a fuel reforming system, and in particular, it is possible to appropriately control the differential pressure between the inside and the outside of a reforming pipe. The present invention relates to an improved fuel reforming system.

(Prior Art) In order to use a raw material gas such as hydrocarbon or methanol as a fuel for a fuel cell, it is necessary to reform these into a hydrogen-rich gas and send them into the fuel cell. It is used.

The general structure of such a fuel reforming system is shown in FIG. That is, in FIG. 3, inside the fuel reforming apparatus 1, a reforming pipe 2 for reforming into hydrogen-rich gas by bringing a mixed gas of raw fuel and steam into contact with a catalyst, and exhaust gas from a fuel cell are provided. A combustor 3 and a combustion chamber 4 that burn are provided. Further, a reaction gas in which a raw fuel such as natural gas and steam for reforming are mixed is introduced into the inside of the reform chamber pipe 2 through a raw fuel control valve 5 and a steam control valve 6, respectively. ing. This reaction gas is heated in the reforming pipe 2 by the combustion gas combusted in the combustor 3 provided in the combustion chamber 4, and is reformed into the reformed gas containing hydrogen as a main component, and then the reformed gas is Carbon oxide transformer 7
Through which the reaction product, carbon monoxide, is converted into carbon dioxide, which is harmless to the fuel cell. Then, in the reformed gas, excess steam introduced for the reforming reaction is removed by condensation in the condenser 8, and the fuel control valve 9
Is supplied to the fuel cell via. Further, the interstitial gas introduced into the fuel cell consumes hydrogen by an electrochemical reaction here, is exhausted, is then introduced into the combustor 3 of the fuel reformer 1, and is supplied through the air regulating valve 11. And is used as a heat source for the reforming. Further, a branch line 16 having a control valve 10 is provided on the upstream side of the fuel control valve 9 so that the reformed gas in the reformed gas line 12 can be discharged to the outside. The control valve 10 discharges the reformed gas when the fuel control valve 9 is closed and the reforming reaction is being performed in the reformer 1, or when the reforming reaction is stopped and the reforming gas is discharged from the inside of the reforming pipe. This is done when it is necessary to reduce the pressure.

In the fuel reforming system as described above, the life of the reforming pipe may be shortened unless the differential pressure between the internal pressure and the external pressure of the reforming pipe is always kept appropriately small to perform the reforming reaction. There is. For example, if the internal pressure of the reforming tube becomes lower than the external pressure at a certain level or more at high temperature, the buckling phenomenon of the reforming tube occurs, and the reforming tube is destroyed. On the contrary, when the internal pressure of the reforming tube becomes higher than a certain level as compared with the internal pressure of the reforming tube, expansion phenomenon of the reforming tube occurs, which may lead to destruction of the reforming tube.

The cause of such an abnormal pressure difference between the inside and outside of the reforming pipe is mainly a transient pressure change that occurs during a sudden load change, when the reformer is stopped, or when the pressure is reduced. When 9 is "closed" or close to this, the pressure inside the reforming pipe and the pressure on the combustor side of the reforming pipe fluctuate independently, so that the internal and external differential pressures of the reforming pipe are abnormal. Can become large.

In order to solve such a problem, conventionally, as shown in FIG. 3, the pressure of the combustion exhaust gas line 13 is improved on the line connecting the reformed gas line 12 and the combustion exhaust gas line 13. The pressure of the reformed gas line 12 and the first safety valve device 14 that operates during that time to discharge the combustion exhaust gas of the combustion exhaust gas line 13 to the outside when the pressure becomes higher than the pressure of the quality gas line 12 by a specified differential pressure or more. Is provided above the pressure of the combustion exhaust gas line 13 by a specified differential pressure or more, a second safety valve device 15 is provided which operates during that time and discharges the reformed gas in the reformed gas line 12 to the outside. The first and second safety valve devices 14 and 15 are mechanical differential pressure safety valves having a structure in which a spring and a diaphragm are combined in the valve body, and a fuel reforming system provided with such a safety valve device is disclosed in 61-
It is proposed in Japanese Patent No. 10876.

(Problems to be Solved by the Invention) However, the conventional fuel reforming system configured as described above has the following problems to be solved.

That is, the first and second safety valve devices as shown in FIG.
Since 14 and 15 are mechanical type differential pressure relief valves, an appropriate dead zone must be provided between the blowout set differential pressure value and the blowoff differential pressure value. If this dead zone is insufficient, the mechanical differential pressure safety valve is apt to cause chattering, and stable differential pressure operation cannot be expected.

On the other hand, in a reformer such as that used in a fuel cell power plant, etc., in particular, the reformer should be reformed as much as possible so that it can be started in a short time and excellent followability to a sudden load change can be obtained. It is necessary to design the wall thickness of the pipe to be small. Therefore, in order to do so, the strength of the reforming pipe at high temperature must be taken into consideration, and the allowable range up to the maximum allowable differential pressure must be made extremely small with respect to the rated internal and external differential pressure during steady operation. However, when the conventional mechanical type differential pressure safety valve as shown in FIG. 3 is used, the dead width between the blow-off and blow-off differential pressures described above is large, and therefore the excessive difference allowed in the reforming pipe is large. There is a problem that it is difficult to put a reforming tube excellent in load followability into practical use because it is unavoidable to increase the allowable range of pressure.

The present invention has been proposed in order to solve the above drawbacks, and its object is a fuel reformer that does not apply a large internal / external differential pressure and enables the practical application of a reforming tube excellent in load followability. To provide a system.

[Configuration of the Invention] (Means for Solving the Problems) The fuel reforming system of the present invention is provided with a differential pressure detector for detecting a differential pressure between the internal pressure and the external pressure of the reforming pipe, and the combustion exhaust gas. A first flow rate control valve branched from the line and a second flow rate control valve branched from the modified glass line, having at least one flow rate control valve; Differential pressure control for comparing a differential pressure signal obtained from the differential pressure detector with a reference differential pressure signal and sending a valve opening signal to the first or second flow rate adjusting valve according to the deviation level thereof. And a device.

(Operation) According to the fuel reforming system of the present invention, the opening degree of the first or second flow rate control valve can be adjusted in accordance with the differential pressure signal between the inside and outside of the reforming pipe. The internal and external differential pressure during operation can be suppressed within an extremely small range even during transient fluctuations.

(Example) Hereinafter, an example of the present invention will be specifically described with reference to FIGS. 1 and 2. The same members as those of the conventional type shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

First Embodiment In this embodiment, as shown in FIG. 1, a first flow rate control valve 20 is provided branching from a combustion exhaust gas line 13.
In addition, the second flow rate control valve is branched from the reformed gas line 12
21 are provided. Further, a differential pressure detector 22 for detecting the differential pressure between the internal pressure and the external pressure of the reforming pipe 2 is provided between the combustion exhaust gas line 13 and the reformed gas line 12, and the differential pressure signal 26 detected here is provided. Is sent to the differential pressure control device 23. Further, the differential pressure control device 23 compares the level of the input detection signal of the differential pressure inside and outside the reforming pipe with a preset reference differential pressure level, and according to the deviation level between the two, the first differential pressure control device Alternatively, the valve opening degrees 24, 25 are delivered to the second flow rate control valves 20, 21.

A PI controller or a digital arithmetic unit may be applied as the differential pressure control device 23, and the differential pressure control device 23 may be configured to have the control function as described above. Also, the first flow control valve
A first reference differential pressure level for adjusting the valve opening of 20,
It is generally different from the second reference differential pressure level for adjusting the valve opening degree of the second flow rate control valve 21.

In the fuel reforming system of this embodiment having such a configuration, the internal / external differential pressure of the reforming pipe is controlled as described below. That is, when the differential pressure of the external pressure of the reforming pipe 1 with respect to the internal pressure transiently exceeds the preset first reference differential pressure, the first flow control valve 20 is opened and the combustion exhaust gas line is opened. Gas is released from 13 to lower the pressure on the combustion exhaust gas side. On the other hand, when the differential pressure of the internal pressure of the reforming pipe 2 with respect to the external pressure exceeds the preset second reference differential pressure, the second flow rate control valve 21 is opened to open the reforming pipe 2. Reduce the inner pressure.

The control parameters (sensitivity and speed of response of the control valves) of the flow rate control valves 20 and 21 in this case can be set relatively freely by the configuration of the differential pressure control device 23, and
Since it is possible to set the first and second reference differential pressures extremely close to the steady-state differential pressure level, the internal and external differential pressures during operation of the reforming pipe can be set within an extremely small range even during transient fluctuations. Can be suppressed within.

As described above, according to the present embodiment, the internal / external pressure difference during the operation of the reforming pipe can be suppressed within an extremely small range even during a transient change, so that the life of the reforming pipe is extended. In addition, the wall thickness of the reforming pipe can be designed thin, and the reforming pipe excellent in load following ability can be put into practical use.

Second Embodiment In this embodiment, as shown in FIG. 2, a temperature detector 30 for measuring the temperature of the reforming pipe 2 is provided, and a temperature signal 31 from the temperature detector 30 causes a differential pressure. It is configured to be sent to the control device 23. In this case, the temperature signal 31 is used to functionally obtain the first or second reference differential pressure signal that serves as a reference for adjusting the valve opening of the first or second flow rate adjusting valve 20, 21. That is, different reference differential pressure levels are created by the preset functional relationship when the detected temperature level of the reforming pipe is high and when the detected temperature level is low, and the flow rate is adjusted by the difference between this and the detected differential pressure signal level. Valve 2
It is configured so that the opening degrees of 0 and 21 can be adjusted.

In the fuel reforming system of this embodiment configured as described above, the differential pressure between the inside and outside of the reforming pipe is controlled as described below. Generally, the permissible fluctuation range of the internal / external differential pressure allowed in the reforming pipe 2 is originally different depending on the temperature level,
If it is attempted to control the differential pressure without depending on the temperature level, it is unavoidable to use an extremely small differential pressure allowable width under the severest maximum temperature. Therefore, for example, even when the load level of the reformer is low and the operating temperature of the reformer is low,
To suppress the differential pressure, the first or second flow rate control valve 2
0 and 21 will be opened and gas will be released outside. On the other hand, according to the present embodiment, when the temperature of the reforming pipe 2 is low, the allowable range of the internal / external differential pressure of the reforming pipe can be made larger than that when the temperature is high, so that the flow rate is unnecessarily increased. Control valve 20,2
1 can be opened to prevent gas from being released to the outside. As a result, the reforming gas and the combustion gas flow rate do not fluctuate greatly even when the differential pressure inside and outside the reforming pipe fluctuates transiently, so that stable operation of the reforming device can be continued.

As described above, according to the present embodiment, in addition to the effect similar to that of the first embodiment, even when there is a transient change in the differential pressure inside and outside the reforming pipe,
It is possible to prevent wasteful emission of the reformed gas and the combustion gas, and perform more stable operation as the reformer.

In the second embodiment, the temperature of the reforming pipe is detected and the reference differential pressure signal of the differential pressure control device is given as a function of the detected temperature. The same effect can be obtained even if the reference differential pressure signal is functionally provided by the above method.

Other Embodiments The present invention is not limited to the first and second embodiments, and at least one of the first and second flow rate control valves may be provided. Further, at least one of the first and second flow rate control valves may be configured as an open / close valve. Even in this case, the same effect can be obtained by appropriately setting the control function of the differential pressure control device.

[Effects of the Invention] As described above, according to the present invention, the opening degree of the first or second flow rate adjusting valve can be adjusted according to the differential pressure signal between the inside and outside of the reforming pipe. By doing so, it is possible to provide a fuel reforming system that does not apply a large pressure difference between the inside and the outside and that can realize the practical use of a reforming tube having excellent load following performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the fuel reforming system of the present invention, FIG. 2 is a block diagram showing a second embodiment of the fuel reforming system of the present invention, and FIG. 3 is a conventional fuel reforming system. It is a block diagram which shows an example of a quality system. 1 ... Fuel reforming device, 2 ... Reforming tube, 3 ... Combustor, 4
…… Fuel chamber, 5 …… Raw fuel control valve, 6 …… Steam control valve, 7 …… Carbon monoxide transformer, 8 …… Condenser, 9 …… Fuel control valve, 10 …… Control valve, 11… … Air control valve, 12 …… Reformed gas line, 13 …… Combustion exhaust gas line, 14 …… First safety valve device, 15 …… Second safety valve device, 16 …… Branch line, 20 …… First Flow rate control valve, 21 ... Second flow rate control valve, 22 ... Differential pressure detector, 23 ... Differential pressure control device, 24,25 ...
… Valve opening signal, 26 …… Differential pressure signal, 30 …… Temperature detector, 31
...... Temperature signal.

Claims (2)

[Claims] 1. A reaction gas obtained by mixing raw fuel and water vapor,
The reaction gas is reformed by introducing the combustion gas into the reforming tube and supplying the fuel and the combustion air to the combustor for combustion to pass the combustion gas through the outer surface of the reforming tube. In a fuel reforming system for reforming into gas, a differential pressure detector for detecting a differential pressure between an internal pressure and an external pressure of the reforming pipe is provided, and a first branch provided by branching from an exhaust gas line of the combustion gas is provided. And a flow rate control valve of at least one of a second flow rate control valve provided by branching from a reformed gas line on the inlet or outlet side of the reforming pipe, Differential pressure control in which a differential pressure signal obtained from the differential pressure detector is compared with a reference differential pressure signal, and a valve opening signal is sent to the first or second flow rate control valve in accordance with the deviation level thereof. And a fuel reforming system characterized by comprising: 2. The fuel reforming system according to claim 1, wherein the reference differential pressure signal of the differential pressure control device is given functionally according to a load level or a temperature level of the fuel reforming device. .