Patent Description:
Conventionally, there has been known a method using a catalyst for producing useful gases such as hydrogen gas and ammonia gas. In this production method, a mixed gas composed of two or more kinds containing a source gas serving as a source of a product gas and an oxidant gas for oxidizing the source gas is introduced as a treatment target gas into a catalyst reaction field, and the treatment target gas is reacted under a high-temperature environment, whereby the product gas is produced.

In a case where the treatment target gas is a mixed gas containing a hydrocarbon-based gas and water vapor or a molecular oxygen containing gas, hydrogen gas can be produced as a product gas (for example, Patent Document <NUM>). In a case where the treatment target gas is a mixed gas containing hydrogen gas and carbon monoxide gas, methane gas, an alcohol, or the like can be produced as a product gas, and in a case where the treatment target gas is a mixed gas containing a hydrocarbon-based gas and air, ammonia gas can be produced as a product gas (for example, Patent Document <NUM>).

In the above mentioned gas production methods, in order to increase the yield (production amount) of the product gas, it is necessary to set the environment of the catalyst reaction field to an extremely high temperature, so that great thermal energy needs to be inputted. Therefore, energy efficiency is low and the production cost for the product gas is high. Accordingly, improvement of energy efficiency in production of the product gas is required.

As an example of a method for improving energy efficiency in production of the product gas, a gas production method using plasma is known, and plasma is also used in Patent Document <NUM> and Patent Document <NUM>. <CIT>relates to a control system for a fuel reformer, and more particularly to a control system for controlling the oxygen-to-carbon ratio of a fuel reformer.

The reason why it is possible to increase the yield of the product gas and improve energy efficiency by using plasma is that not only a gas reactive material in the treatment target gas can be excited by the plasma but also highly reactive chemical species such as ions and radicals are formed on the catalyst surface by the plasma.

However, in a conventional gas production system using catalyst reaction and plasma, the mixed gas composed of two or more kinds containing a source gas serving as a source of the product gas and an oxidant gas for oxidizing the source gas continues to be supplied as the treatment target gas. Therefore, while there is a possibility that the gas reactive material in the treatment target gas can be excited by the plasma, the effect of forming the highly reactive chemical species such as ions or radicals on the catalyst surface is not obtained sufficiently, so that improvement of the yield of the product gas and energy efficiency might be suppressed.

The present invention has been made to solve the above problem, and an object of the present invention is to provide a gas production system and a gas production method that can improve the yield of the product gas and energy efficiency by efficiently promoting formation of highly reactive chemical species on the catalyst surface.

According to the invention, the problem is solved by the subject matter outlined in independent claims <NUM> and <NUM>. Advantageous further developments of the invention are set forth in the dependent claims.

The gas production system and the gas production method according to the present invention can efficiently promote formation of highly reactive chemical species on the catalyst surface, thus making it possible to provide a gas production system and a gas production method that can improve the yield of the product gas and energy efficiency.

Hereinafter, embodiments of a gas production system and a gas production method will be described with reference to the drawings. It is noted that the embodiments described below are merely examples and are not intended to limit the present invention. In the drawings, the same reference characters denote the same or corresponding parts.

Hereinafter, a gas production system according to Embodiment <NUM> will be described. <FIG> schematically shows the configuration of the gas production system according to Embodiment <NUM>. The gas production system includes: a gas production device <NUM> having a reactor <NUM>, a first electrode <NUM> and a second electrode <NUM> for generating plasma, and a catalyst layer <NUM>; an external power supply <NUM> connected to the first electrode <NUM> and the second electrode <NUM> and configured to supply power; source gas supply means <NUM> for supplying a source gas <NUM> to the reactor <NUM>; oxidant gas supply means <NUM> for supplying an oxidant gas <NUM> to the reactor <NUM>; and the like. In <FIG>, the cross section of the gas production device <NUM> is shown.

The gas production device <NUM> includes a supply portion <NUM> and a flow-out portion <NUM>, and the supply portion <NUM> and the flow-out portion <NUM> are connected to the reactor <NUM>. The source gas <NUM> and the oxidant gas <NUM> are supplied from the supply portion <NUM> to the reactor <NUM>. The reactor <NUM> forms a flow path <NUM> through which the source gas <NUM> and the oxidant gas <NUM> flow. The first electrode <NUM> is provided inside the reactor <NUM>, and the second electrode <NUM> is provided outside the reactor <NUM>.

The second electrode <NUM> is grounded, and the first electrode <NUM> is connected to the reactor <NUM> via a supporter <NUM> and is fixed in a state of being insulated from the second electrode <NUM>. In a space between the first electrode <NUM> and the second electrode <NUM> in the flow path <NUM>, the catalyst layer <NUM> is provided and includes a catalyst for causing a reaction of reforming the source gas <NUM> and the oxidant gas <NUM> into a product gas <NUM>. The product gas <NUM> reformed through the catalyst reaction in the catalyst layer <NUM> is sent through the flow-out portion <NUM> to the outside of the gas production device <NUM>.

The first electrode <NUM> and the second electrode <NUM> are connected to the external power supply <NUM>, and the external power supply <NUM> generates high voltage to generate plasma in the space between the first electrode <NUM> and the second electrode <NUM>. The type of the plasma is not particularly limited, but in terms of energy efficiency, a preferable type is non-equilibrium plasma in which the electron temperature is much higher than the gas temperature and thus the catalyst reaction of the source gas <NUM> and the oxidant gas <NUM> can be activated at a comparatively low temperature.

The configuration of the gas production device <NUM> is not particularly limited as long as the gas production device <NUM> includes the reactor <NUM>, the first electrode <NUM>, and the second electrode <NUM>, and the source gas <NUM> and the oxidant gas <NUM> are supplied to the catalyst layer <NUM> provided in the space between the first electrode <NUM> and the second electrode <NUM>.

However, in order to efficiently activate the catalyst reaction of the source gas <NUM> and the oxidant gas <NUM>, it is preferable that the plasma can be generated along the surface of the catalyst in the catalyst layer <NUM>, and it is preferable that the gas production device <NUM> has a cylindrical shape. <FIG> schematically shows a sectional view along line X-X in <FIG>. As shown in <FIG>, it is preferable that the reactor <NUM> and the second electrode <NUM> have cylindrical shapes, the reactor <NUM> is coated with the second electrode <NUM>, and the first electrode <NUM> has a bar shape and is placed on the center axis of the reactor <NUM>.

The materials of the first electrode <NUM> and the second electrode <NUM> are not particularly limited as long as they can generate plasma with high voltage from the external power supply <NUM>, and may be known materials such as copper, iron, and tungsten. In view of corrosion of the electrodes, an alloy such as stainless steel resistant to corrosion is preferably used. In addition, the material of the reactor <NUM> is preferably a dielectric material, and may be a known material such as ceramic or glass.

The form of the catalyst forming the catalyst layer <NUM> is not particularly limited, and may be a pellet form, a granular form, or the like.

While the source gas <NUM> and the oxidant gas <NUM> are being supplied from the supply portion <NUM> into the reactor <NUM>, when high voltage is generated by the external power supply <NUM>, plasma can be generated in the catalyst layer <NUM> provided in the space between the first electrode <NUM> and the second electrode <NUM> in the reactor <NUM>. In the catalyst layer <NUM>, the source gas <NUM> and the oxidant gas <NUM> are reformed into the product gas <NUM>.

The source gas <NUM> is supplied to the reactor <NUM> by the source gas supply means <NUM>, and the oxidant gas <NUM> is supplied to the reactor <NUM> by the oxidant gas supply means <NUM>. As shown in <FIG>, gas ratio change means <NUM> having a function of controlling the supply amount of the source gas <NUM> and changing the supply amount is provided between the source gas supply means <NUM> and the supply portion <NUM>.

The gas ratio change means <NUM> prescribes one cycle and a reference supply amount of the source gas <NUM>, sets a time ST for supplying the source gas <NUM> in the reference supply amount and a time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount in the one cycle, and repeatedly executes such an operation. Thus, the ratio between the supply amount of the source gas <NUM> to the reactor <NUM> and the supply amount of the oxidant gas <NUM> to the reactor <NUM> can be changed.

Regarding the changing of the ratio between the supply amount of the source gas <NUM> and the supply amount of the oxidant gas <NUM>, the gas ratio change means <NUM> may prescribe one cycle and a reference supply amount of the oxidant gas <NUM>, set a time STO for supplying the oxidant gas <NUM> in the reference supply amount and a time CTO for supplying the oxidant gas <NUM> in a supply amount larger than the reference supply amount in the one cycle, and repeatedly execute such an operation.

Further, the gas ratio change means <NUM> may perform control so as to change the supply amounts of both the source gas <NUM> and the oxidant gas <NUM>. Although the gas ratio change means <NUM> is provided between the supply portion <NUM>, and the source gas supply means <NUM> and the oxidant gas supply means <NUM> in <FIG>, the source gas supply means <NUM> or the oxidant gas supply means <NUM> may have the function of the gas ratio change means <NUM>, or both of them may have the function. In this case, the gas ratio change means <NUM> may be provided in the source gas supply means <NUM> or the oxidant gas supply means <NUM>, or may be provided in both of them.

When the source gas <NUM> is supplied in the reference supply amount, gas reactive materials in the oxidant gas <NUM> and the source gas <NUM> can be efficiently excited by the plasma. On the other hand, when the source gas <NUM> is supplied in a supply amount smaller than the reference supply amount, the oxidant gas <NUM> is made abundant as compared to the source gas <NUM>, so that the oxidant gas <NUM> is more likely to be excited by the plasma.

Thus, formation of active oxygen species which are highly reactive chemical species is promoted on the catalyst surface in the catalyst layer <NUM>. In a state in which active oxygen species which are highly reactive chemical species are formed on the catalyst surface in the catalyst layer <NUM>, if supply of the source gas <NUM> in the reference supply amount is restarted (the next cycle begins), the synergistic effect of the plasma and the catalyst reaction increases, whereby the yield of the product gas and energy efficiency can be improved.

The external power supply <NUM> for generating high voltage is not particularly limited and may be a known power supply such as an AC power supply or a pulse power supply. Therefore, the signal waveform of the external power supply <NUM> may be a sine wave, a pulse wave, a rectangular wave, or the like, and is not particularly limited.

In addition, the magnitude of high voltage generated by the external power supply <NUM> is not particularly limited as long as plasma can be generated in the space between the first electrode <NUM> and the second electrode <NUM>. However, if the magnitude of the high voltage is extremely low, plasma cannot be generated, and conversely, if the magnitude of the high voltage is extremely high, power consumption increases and energy efficiency is reduced. Therefore, the magnitude of the high voltage is preferably not less than <NUM> kV and not greater than <NUM> kV, and more preferably not less than <NUM> kV and not greater than <NUM> kV.

The time ST for supplying the source gas <NUM> in the reference supply amount, and a ratio ST/CT of the time ST for supplying the source gas <NUM> in the reference supply amount to the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount, can be set as appropriate in consideration of the amount of the prepared source gas <NUM>, the planned amount of the product gas <NUM>, and the like, and are not particularly limited.

However, if the time ST for supplying the source gas <NUM> in the reference supply amount is extremely long, there is a possibility that the amount of chemical species on the catalyst surface in the catalyst layer <NUM> is reduced to be insufficient. Meanwhile, if the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount is long and thus ST/CT is small, the amount of the product gas <NUM> decreases and production performance for the product gas <NUM> is reduced.

Therefore, the time ST for supplying the source gas <NUM> in the reference supply amount is preferably not less than <NUM> minutes and not greater than <NUM> minutes, and more preferably not less than <NUM> minutes and not greater <NUM> minutes. In addition, the ratio ST/CT is preferably not less than <NUM> and not greater than <NUM>, and more preferably not less than <NUM> and not greater than <NUM>.

As the frequency of the high voltage of the external power supply <NUM> becomes higher, the density of electrons in the generated plasma becomes greater, and therefore, the effect of promoting formation of highly reactive chemical species on the catalyst surface in the catalyst layer <NUM> by the plasma when the source gas <NUM> is supplied in a supply amount smaller than the reference supply amount, is increased.

However, if the frequency of the high voltage of the external power supply <NUM> is higher than necessary, the density of electrons becomes excessive, and power consumption needed for generating plasma increases, so that energy efficiency can be reduced. Therefore, the frequency of the high voltage of the external power supply <NUM> is preferably not less than <NUM> and not greater than <NUM>.

In addition, in consideration of the influence of the frequency, the time ST for supplying the source gas <NUM> in the reference supply amount and the ratio ST/CT of the time ST for supplying the source gas <NUM> in the reference supply amount to the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount may be adjusted in accordance with the frequency of the high voltage of the external power supply <NUM>.

For example, in a case where the frequency of the high voltage of the external power supply <NUM> is low, in order to ensure the effect of promoting formation of chemical species on the catalyst surface in the catalyst layer <NUM>, the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount is increased to reduce the ratio ST/CT. In a case where the frequency of the high voltage of the external power supply <NUM> is high, in order to suppress reduction in energy efficiency due to increased power consumption needed for generating plasma, the time ST for supplying the source gas <NUM> in the reference supply amount can be increased.

Also for the prescribed reference supply amount of the source gas <NUM> from the source gas supply means <NUM>, the value thereof may be set as appropriate in consideration of the amount of the prepared source gas <NUM>, the planned amount of the product gas <NUM>, or the like, and is not particularly limited. However, in consideration of reaction efficiency of the source gas <NUM> and the oxidant gas <NUM>, it is preferable that the reference supply amount of the source gas <NUM> is determined on the basis of a stoichiometric ratio determined by the kinds and reaction of the source gas <NUM> and the oxidant gas <NUM>.

For example, in a case where the source gas <NUM> is hydrogen, the oxidant gas <NUM> is carbon monoxide, and the product gas <NUM> is methane, the main reaction is represented by the following Expression (<NUM>). Therefore, preferably, the reference supply amount is determined such that the partial pressure of hydrogen which is the source gas <NUM> is three times the partial pressure of carbon monoxide which is the oxidant gas <NUM>. Thus, during the time for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount, a state in which the oxidant gas <NUM> is abundant as compared to the source gas <NUM> can easily be made.

<NUM><NUM> + CO → CH<NUM> + H<NUM>O.

The source gas supply means <NUM> and the oxidant gas supply means <NUM> may be any means and have any configurations as long as the source gas <NUM> and the oxidant gas <NUM> can be supplied to the reactor <NUM>. For example, in a case where the source gas <NUM> and the oxidant gas <NUM> are stored as high-pressure gases in cylinders, the source gas <NUM> and the oxidant gas <NUM> can be supplied to the reactor <NUM> owing to the pressure difference between the cylinders and the gas production device <NUM>. In a case where a gas transportation device such as a pump is provided, the source gas <NUM> and the oxidant gas <NUM> can be supplied to the reactor <NUM> by operation of the gas transportation device.

The gas ratio change means <NUM> may be any means as long as the supply amount of the source gas <NUM> to the reactor <NUM> can be controlled and changed or the ratio of the supply amounts of the source gas <NUM> and the oxidant gas <NUM> can be controlled and changed. A known device for controlling a gas flow rate, such as a flow regulating valve or a mass flow controller, can be used. Instead of supplying the source gas <NUM> in a supply amount smaller than the reference supply amount, supply of the source gas <NUM> may be completely stopped.

<FIG> is a chart showing an operation flow of the gas production system according to Embodiment <NUM>, and shows a production method for the product gas. This gas production method includes a source gas supply step, an oxidant gas supply step, a plasma application step, a reforming step, and a gas ratio change step.

First, in step S1, whether or not active oxygen species are sufficiently present on the catalyst surface in the catalyst layer <NUM> in the reactor <NUM> is determined, and if it is determined that active oxygen species are sufficiently present (YES in step S1), the process proceeds to step S4. If active oxygen species are not sufficiently present on the catalyst surface (NO in step S1), in step S2, the oxidant gas <NUM> is supplied to the catalyst layer <NUM> in the reactor <NUM> by the oxidant gas supply means <NUM>, and high voltage is applied between the first electrode <NUM> and the second electrode <NUM> by the external power supply <NUM>, to generate plasma in the catalyst layer <NUM>.

By the generation of plasma, active oxygen species are formed on the catalyst surface in the catalyst layer <NUM>. The determination as to whether active oxygen species are sufficiently present on the catalyst surface in the catalyst layer <NUM> in the reactor <NUM> in step S1 may be made on the basis of the elapsed time since the last operation of the gas production system, or elapse of time or the processing sequence indicating whether or not the last operation of the gas production system was ended after active oxygen species were formed on the catalyst surface, for example. The above step S2 is an example of the oxidant gas supply step and the plasma application step.

Step S3 is a step of determining whether or not active oxygen species are sufficiently formed on the catalyst surface in the catalyst layer <NUM> through the processing in step S2, and this can be determined on the basis of whether or not a processing time t0 in step S2 has reached a predetermined time CT, for example. Here, the time CT is the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount as described above, but is not limited thereto. Step S2 is repeated until the processing time t0 reaches the time CT or it is determined that active oxygen species are sufficiently formed.

In the next step S4, to the catalyst layer <NUM> in the reactor <NUM>, the source gas <NUM> is supplied in the prescribed reference supply amount by the source gas supply means <NUM> and the oxidant gas <NUM> is supplied by the oxidant gas supply means <NUM>, and high voltage is applied between the first electrode <NUM> and the second electrode <NUM> by the external power supply <NUM>, whereby plasma is generated and thus the plasma is applied to the catalyst layer <NUM>. After the step S3, generation of plasma may be stopped, or the plasma may continue to be generated until this step S4. This step S4 includes examples of the source gas supply step, the oxidant gas supply step, and the plasma application step. In step S4 including these three steps, the product gas <NUM> is produced from the source gas <NUM> and the oxidant gas <NUM> in the catalyst layer <NUM>.

In step S5, whether or not the processing time t1 in step S4 has reached the time ST for supplying the source gas <NUM> in the reference supply amount in one cycle prescribed by the gas ratio change means <NUM> is determined, and until the time ST is reached, the process returns to step S4 and the processing in step S4 is continued. The processing in step S4 that is being continued is an example of the reforming step. If the processing time t1 in step S4 has reached the time ST (YES in step S5), the process proceeds to the next step S6.

In step S6, if the product gas <NUM> generated by reformation of the source gas <NUM> and the oxidant gas <NUM> has reached a planned production amount (YES in step S6), the process proceeds to step S9. If the product gas <NUM> has not reached the planned production amount (NO in step S6), the process proceeds to step S7.

In step S7, by the source gas supply means <NUM>, the supply amount of the source gas <NUM> is decreased to a value smaller than the reference supply amount prescribed in advance, or supply of the source gas <NUM> is stopped. This step S7 is an example of the gas ratio change step, and in this step, formation of active oxygen species is promoted on the catalyst surface in the catalyst layer <NUM> in the reactor <NUM>.

In step S8, whether or not a processing time t2 in step S5 has reached the time CT for supplying the source gas <NUM> in a supply amount smaller than the reference supply amount in one cycle prescribed by the gas ratio change means <NUM>, is determined, and until the time CT is reached, the process returns to step S7 and the processing is continued. If the processing time t2 in step S7 has reached the time CT (YES in step S8), the process returns to step S4, to set the supply amount of the source gas <NUM> to the reference supply amount.

The reforming step processing in step S4 and the gas ratio change step processing in step S7 are repeatedly executed during the time ST and the time CT in one cycle prescribed by the gas ratio change means <NUM>, to produce the product gas <NUM> until reaching the planned product gas amount.

If the produced product gas <NUM> has reached the planned product gas amount, in step S9, application of high voltage between the first electrode <NUM> and the second electrode <NUM> is stopped by the external power supply <NUM>, so that generation of plasma is stopped. Supply of the source gas <NUM> and the oxidant gas <NUM> is stopped by the source gas supply means <NUM> and the oxidant gas supply means <NUM>, respectively. Thus, a series of gas production steps is finished.

In the process of the gas production method described above, step S6 may be performed at a stage subsequent to step S8, to determine whether or not the planned product gas amount has been reached per one cycle prescribed by the gas ratio change means <NUM>. In this case, the process is finished in a state in which active oxygen species are formed on the catalyst surface in the catalyst layer <NUM> in the reactor <NUM>, and therefore it becomes possible to skip step S2 or shorten the processing time in step S2, in the next operation of the gas production system.

In step S7, the case of performing the gas ratio change step by changing the supply amount of the source gas <NUM> from that in step S4 has been described as an example. However, as described above, the supply amount of the oxidant gas <NUM> may be used as a reference. That is, the process may be performed such that, in step S4, the oxidant gas <NUM> is supplied in a reference supply amount during the time STO, and in step S7, the oxidant gas <NUM> is supplied in a supply amount larger than the reference supply amount during the time CTO. Further, the gas ratio change means <NUM> may perform control so as to change both supply amounts of the source gas <NUM> and the oxidant gas <NUM>.

As described above, according to Embodiment <NUM>, the gas production system includes the gas ratio change means <NUM> capable of changing the ratio between the source gas <NUM> and the oxidant gas <NUM>, whereby a state in which the oxidant gas <NUM> for oxidizing the source gas <NUM> is abundant as compared to the source gas <NUM> can be made and formation of active oxygen species which are highly reactive chemical species is promoted on the catalyst surface in the catalyst layer <NUM>. Thus, the synergistic effect of the plasma and catalyst reaction is increased, so that the yield of the product gas <NUM> and energy efficiency can be improved.

In Embodiment <NUM>, it has been described that the cross sections of the reactor <NUM> and the second electrode <NUM> have annular shapes, the reactor <NUM> is coated with the second electrode <NUM>, and the first electrode <NUM> has a bar shape and is placed on the center axis of the reactor <NUM>, as an example of the configuration. However, the present invention is not limited to the above example. For example, the cross sections of the reactor <NUM> and the second electrode <NUM> may be rectangular shapes as long as the same function is obtained.

Hereinafter, a gas production system according to Embodiment <NUM> will be described. The configuration and the operation of the gas production system according to Embodiment <NUM> are basically the same as those in Embodiment <NUM>, while a difference is that the gas production system according to Embodiment <NUM> includes: a second gas production device <NUM> having the same components as in the gas production device <NUM>; a second external power supply <NUM> for supplying power to the second gas production device <NUM>; a source gas branch portion <NUM> for supplying the source gas <NUM> to the second gas production device <NUM>; second source gas supply means <NUM>; an oxidant gas branch portion <NUM> for supplying the oxidant gas <NUM> to the second gas production device <NUM>; second oxidant gas supply means <NUM>; and second gas ratio change means <NUM>.

<FIG> schematically shows the configuration of the gas production system according to Embodiment <NUM>. In the drawing, the same components and members as those of the gas production system according to Embodiment <NUM> are denoted by the same reference characters, and description thereof is omitted unless particularly needed. In <FIG>, the gas production system according to Embodiment <NUM> includes, in addition to the gas production device <NUM>, the second gas production device <NUM> having the same components as those of the gas production device <NUM>.

That is, the second gas production device <NUM> includes all the components corresponding to the reactor <NUM>, the first electrode <NUM>, the second electrode <NUM>, the catalyst layer <NUM>, the supply portion <NUM>, the flow-out portion <NUM>, the flow path <NUM>, and the supporter <NUM>, and is the same mechanism as the gas production device <NUM>. Thus, high voltage is applied by the second external power supply <NUM> so as to generate plasma in the reactor <NUM>, whereby a second product gas <NUM> can be obtained. In the present embodiment, the gas production devices <NUM>, <NUM> produce the same gases, i.e., the product gases <NUM>, <NUM> are equivalent.

In addition, since the source gas branch portion <NUM>, the second source gas supply means <NUM>, the oxidant gas branch portion <NUM>, and the second oxidant gas supply means <NUM> are provided, the source gas <NUM> and the oxidant gas <NUM> can be supplied to not only the gas production device <NUM> but also the second gas production device <NUM>. Further, by the second gas ratio change means <NUM>, the supply amount of the source gas <NUM> to the second gas production device <NUM> can be controlled and changed independently of the gas ratio change means <NUM>.

With the gas production device <NUM> and the second gas production device <NUM> provided, production performance for the product gases <NUM>, <NUM> can be enhanced. That is, while, in the gas production device <NUM>, the source gas <NUM> is being supplied in a supply amount smaller than the reference supply amount so as to make the oxidant gas <NUM> abundant as compared to the source gas <NUM> and thus formation of chemical species is being promoted on the catalyst surface in the catalyst layer <NUM> (gas ratio change step), the source gas <NUM> can be supplied in the reference supply amount in the second gas production device <NUM> to produce the second product gas <NUM> (gas reforming step).

Conversely, while, in the second gas production device <NUM>, the source gas <NUM> is being supplied in a supply amount smaller than the reference supply amount (gas ratio change step), the source gas <NUM> can be supplied in the reference supply amount in the gas production device <NUM> to produce the product gas <NUM> (gas reforming step).

In the gas production device <NUM>, during the gas ratio change step, the amount of the product gas <NUM> is decreased and production performance for the product gas <NUM> is reduced. During this period, in the second gas production device <NUM>, the second product gas <NUM> can be produced in the gas reforming step. Subsequently, in the gas production device <NUM>, the gas reforming step is performed under high catalyst activity, whereby the product gas <NUM> is efficiently produced, and during this period, in the second gas production device <NUM>, the gas ratio change step is performed so that formation of chemical species for activating the catalyst surface is promoted. Thus, production performance for the product gases <NUM>, <NUM> can be enhanced.

That is, while production performance for the product gas <NUM> is being reduced in the gas production device <NUM> in order to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction by maintaining high catalyst activity, production performance for the second product gas <NUM> can be ensured in the second gas production device <NUM>, and while production performance for the product gas <NUM> is being ensured in the gas production device <NUM>, high catalyst activity can be maintained in the second gas production device <NUM> so as to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction. Thus, production performance for the product gas in the gas production system can be enhanced, and the yield of the product gas and energy efficiency can be improved.

Next, the supply time for the source gas <NUM> will be discussed.

A time ST1 for supplying the source gas <NUM> to the gas production device <NUM> in the reference supply amount, a ratio ST1/CT1 of the time for supplying the source gas <NUM> to the gas production device <NUM> in the reference supply amount to a time CT1 for supplying the source gas <NUM> to the gas production device <NUM> in a supply amount smaller than the reference supply amount, a time ST2 for supplying the source gas <NUM> to the second gas production device <NUM> in the reference supply amount, and a ratio ST2/CT2 of the time for supplying the source gas <NUM> to the second gas production device <NUM> in the reference supply amount to a time CT2 for supplying the source gas <NUM> to the second gas production device <NUM> in a supply amount smaller than the reference supply amount, can be set as appropriate in consideration of the amount of the prepared source gas <NUM>, the planned amounts of the product gases <NUM>, <NUM>, and the like in the gas production device <NUM> and the second gas production device <NUM>, and are not particularly limited.

However, in terms of production performance for the product gas, it is preferable that CT1 and ST2 are the same value and ST1 and CT2 are the same value. Thus, the product gas (product gas <NUM> or second product gas <NUM>) can be continuously produced. In addition, for example, in a case where the product gas <NUM> and the second product gas <NUM> are to be produced in the same amount, ST1, CT1, ST2, and CT2 may be equal.

The configurations and the materials of the components of the second gas production device <NUM> need not be completely the same as those of the gas production device <NUM> as long as equivalent functions can be obtained. In addition to the second gas production device <NUM>, a plurality of gas production devices having the same components as those of the gas production device <NUM> may be further provided.

As described above, the gas production system according to Embodiment <NUM> can provide the same effects as in Embodiment <NUM>.

Further, in the gas production system according to Embodiment <NUM>, the second gas production device <NUM> having a configuration equivalent to the gas production device <NUM> is provided, the source gas <NUM> and the oxidant gas <NUM> can be supplied to both of the gas production device <NUM> and the second gas production device <NUM>, and the second gas ratio change means <NUM> is provided, whereby the supply amount of the source gas <NUM> to the second gas production device <NUM> can be changed and the ratio between the source gas <NUM> and the oxidant gas <NUM> can be changed.

Thus, while the gas ratio change step is being performed in the gas production device <NUM>, the second gas production device <NUM> produces the second product gas <NUM> in the gas reforming step. Then, in the gas production device <NUM>, the product gas <NUM> is effectively produced during the gas reforming step under high catalyst activity, and during this period, the gas ratio change step is performed in the second gas production device <NUM> to promote formation of chemical species for activating the catalyst surface. In this way, production performance for the product gases <NUM>, <NUM> can be enhanced.

That is, while high catalyst activity is being maintained in the gas production device <NUM> to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction, production performance can be ensured in the second gas production device <NUM>, and while production performance is being ensured in the gas production device <NUM>, high catalyst activity can be maintained in the second gas production device <NUM> to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction. Therefore, production performance for the product gas in the gas production system can be enhanced, and the yield of the product gas and energy efficiency can be improved.

In the above description, the example in which the number of the gas production devices, i.e., the reactors having the catalyst layers, is two has been shown. However, three or more reactors may be provided. In a case of providing three or more reactors, the processing steps for the reactors may be sequentially switched so that, while at least one of the plurality of reactors is undergoing the source gas supply step, not all the other reactors undergo the source gas supply step. For example, the steps can be sequentially switched as follows.

When the first gas production device undergoes the source gas supply step and then the gas reforming step is finished, next, the second gas production device is switched from the gas ratio change step to the source gas supply step. Then, when the source gas supply step and the gas reforming step are finished in the second gas production device, next, the third gas production device is switched from the gas ratio change step to the source gas supply step. In a case of providing four reactors, they may be divided into two groups, and the steps may be switched between the first group and the second group.

Hereinafter, a gas production system according to Embodiment <NUM> will be described. The configuration and the operation of the gas production system according to Embodiment <NUM> are basically the same as those in Embodiment <NUM>, but Embodiment <NUM> shows an example in which a hydrocarbon-based gas <NUM> is supplied as the source gas <NUM> to the gas production device <NUM> or the second gas production device <NUM>, a hydrogen containing gas <NUM> is produced as the product gas <NUM>, and a second hydrogen containing gas <NUM> is produced as the second product gas <NUM>.

<FIG> schematically shows the configuration of the gas production system according to Embodiment <NUM>. In the drawing, the same components and members as those of the gas production system according to Embodiment <NUM> are denoted by the same reference characters, and description thereof is omitted unless particularly needed.

In the gas production system according to Embodiment <NUM>, the hydrocarbon-based gas <NUM> and the oxidant gas <NUM> are supplied from the supply portion <NUM> to the gas production device <NUM>. While the hydrocarbon-based gas <NUM> and the oxidant gas <NUM> are being supplied from the supply portion <NUM> to the gas production device <NUM>, high voltage is applied between the first and second electrodes <NUM> and <NUM> by the external power supply <NUM>, to generate plasma in the catalyst layer <NUM>.

The hydrocarbon-based gas <NUM> and the oxidant gas <NUM> react in the catalyst layer <NUM> so as to be reformed, whereby the hydrogen containing gas <NUM> is produced. Similarly, also in the second gas production device <NUM>, while the hydrocarbon-based gas <NUM> and the oxidant gas <NUM> are being supplied to the second gas production device <NUM>, high voltage is applied by the second external power supply <NUM>, to generate plasma, and the second hydrogen containing gas <NUM> is produced from the hydrocarbon-based gas <NUM> and the oxidant gas <NUM>.

With the gas production device <NUM> and the second gas production device <NUM> provided, production performance for the hydrogen containing gases <NUM>, <NUM> can be enhanced. That is, while, in the gas production device <NUM>, the hydrocarbon-based gas <NUM> is being supplied in a supply amount smaller than the reference supply amount so as to make the oxidant gas <NUM> abundant as compared to the source gas <NUM> and thus formation of chemical species is being promoted on the catalyst surface in the catalyst layer <NUM> (gas ratio change step), the hydrocarbon-based gas <NUM> can be supplied in the reference supply amount in the second gas production device <NUM> to produce the second hydrogen containing gas <NUM> (gas reforming step).

Conversely, while, in the second gas production device <NUM>, the hydrocarbon-based gas <NUM> is being supplied in a supply amount smaller than the reference supply amount (gas ratio change step), the hydrocarbon-based gas <NUM> can be supplied in the reference supply amount in the gas production device <NUM> to produce the hydrogen containing gas <NUM> (gas reforming step).

In the gas production device <NUM>, during the gas ratio change step, the production amount of the hydrogen containing gas <NUM> is decreased and production performance for the product gas <NUM> is reduced. During this period, in the second gas production device <NUM>, the second hydrogen containing gas <NUM> can be produced in the gas reforming step.

Subsequently, in the gas production device <NUM>, the gas reforming step is performed under high catalyst activity, whereby the hydrogen containing gas <NUM> is efficiently produced, and during this period, in the second gas production device <NUM>, the gas ratio change step is performed so that formation of chemical species for activating the catalyst surface is promoted.

Thus, production performance for the hydrogen containing gases <NUM>, <NUM> can be enhanced. That is, while production performance for the hydrogen containing gas <NUM> is being reduced in the gas production device <NUM> in order to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction by maintaining high catalyst activity, production performance for the second hydrogen containing gas <NUM> can be ensured in the second gas production device <NUM>, and while production performance for the hydrogen containing gas <NUM> is being ensured in the gas production device <NUM>, high catalyst activity can be maintained in the second gas production device <NUM> so as to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction. Thus, production performance for the product gas in the gas production system can be enhanced, and the yield of the product gas and energy efficiency can be improved.

The hydrocarbon-based gas <NUM> is not particularly limited as long as the hydrocarbon-based gas <NUM> contains a carbon atom and a hydrogen atom and can be reformed into a hydrogen containing gas. For example, a hydrocarbon such as methane, ethane, or propane, an alcohol such as methanol or ethanol, or the like can be used.

Also the oxidant gas <NUM> is not particularly limited as long as the oxidant gas <NUM> can react with the hydrocarbon-based gas <NUM> and thus a hydrogen containing gas can be produced. Water vapor obtained by vaporizing water or a molecular oxygen containing gas such as carbon monoxide can be used. However, in terms of reactivity of the hydrocarbon-based gas <NUM> and the oxidant gas <NUM>, it is preferable that the oxidant gas <NUM> is one kind of gas or a mixed gas of two or more kinds of gases, selected from water vapor, carbon dioxide gas, and oxygen gas.

Also for the reference supply amount of the hydrocarbon-based gas <NUM> prescribed by the gas ratio change means <NUM>, the value thereof may be set as appropriate in consideration of the amount of the prepared hydrocarbon-based gas <NUM>, the planned production amount of the hydrogen containing gas <NUM>, or the like, and is not particularly limited. However, in consideration of reaction efficiency of the hydrocarbon-based gas <NUM> and the oxidant gas <NUM>, it is preferable that the reference supply amount of the hydrocarbon-based gas <NUM> is determined on the basis of a stoichiometric ratio determined by the kinds and reaction of the hydrocarbon-based gas <NUM> and the oxidant gas <NUM>.

For example, in a case where the hydrocarbon-based gas <NUM> is methane and the oxidant gas <NUM> is carbon dioxide, the main reaction is represented by the following Expression (<NUM>). Therefore, preferably, the reference supply amount is determined such that the partial pressure of the hydrocarbon-based gas <NUM> is as great as the partial pressure of the oxidant gas <NUM>. Thus, during the time for supplying the hydrocarbon-based gas <NUM> in a supply amount smaller than the reference supply amount, a state in which the oxidant gas <NUM> is abundant as compared to the hydrocarbon-based gas <NUM> can be easily made.

CH<NUM> + CO<NUM> → 2CO + <NUM><NUM>.

The reaction in which the hydrogen containing gas <NUM> is produced in the catalyst layer <NUM> of the gas production device <NUM> is formed from, in addition to a reaction in which the hydrocarbon-based gas <NUM> is oxidized by the oxidant gas <NUM> to generate hydrogen, a reaction in which the hydrocarbon-based gas <NUM> is decomposed to generate hydrogen, for example. At this time, carbon which constitutes the hydrocarbon-based gas <NUM> might be deposited on the catalyst surface.

The carbon deposited on the catalyst surface inhibits the reaction for producing the hydrogen containing gas <NUM>, and this can lead to reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM>. In a case where the hydrocarbon-based gas <NUM> is methane and the oxidant gas <NUM> is carbon dioxide, a reaction in which the hydrocarbon-based gas <NUM> is decomposed to generate hydrogen is represented by the following Expression (<NUM>).

CH<NUM> → <NUM><NUM> + C.

Thus, carbon (C) is deposited on the catalyst surface.

However, when the supply amount of the hydrocarbon-based gas <NUM> to the gas production device <NUM> is changed so that the ratio of the oxidant gas <NUM> to the hydrocarbon-based gas <NUM> is changed, and plasma is generated in a state in which the oxidant gas <NUM> for oxidizing the hydrocarbon-based gas <NUM> is abundant as compared to the hydrocarbon-based gas <NUM> (gas ratio change step), formation of active oxygen species which are highly reactive chemical species is promoted on the catalyst surface in the catalyst layer <NUM> and also a reaction of forming an oxide on the catalyst surface occurs. Owing to the formed oxide, it is possible to inhibit deposition of carbon on the catalyst surface when the hydrocarbon-based gas <NUM> is supplied in the reference supply amount (gas reforming step). Thus, the yield of hydrogen gas in the hydrogen containing gas <NUM> can be further improved and also energy efficiency can be further improved.

In the present embodiment, the kind of the catalyst is not particularly limited as long as the hydrocarbon-based gas <NUM> can be reformed into the hydrogen containing gas, and a known catalyst can be used. However, in terms of reactivity, it is preferable to use a catalyst containing a transition metal element such as nickel, iron, or cobalt.

Further, in the gas production system according to Embodiment <NUM>, the hydrocarbon-based gas <NUM> is used as the source gas. While the gas ratio change step is being performed in the gas production device <NUM>, the second gas production device <NUM> produces the second hydrogen containing gas <NUM> in the gas reforming step. Then, in the gas production device <NUM>, the hydrogen containing gas <NUM> is effectively produced during the gas reforming step under high catalyst activity, and during this period, the gas ratio change step is performed in the second gas production device <NUM> to promote formation of chemical species for activating the catalyst surface.

In this way, production performance for the hydrogen containing gases <NUM>, <NUM> can be enhanced. That is, while high catalyst activity is being maintained in the gas production device <NUM> to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction, production performance can be ensured in the second gas production device <NUM>, and while production performance is being ensured in the gas production device <NUM>, high catalyst activity can be maintained in the second gas production device <NUM> to obtain an effect of increasing the synergistic effect of plasma and catalyst reaction.

Therefore, production performance for the product gas in the gas production system can be enhanced, and the yield of the product gas (hydrogen containing gas) and energy efficiency can be improved. In addition, in the gas production device <NUM> and the second gas production device <NUM>, during the gas ratio change step, an oxide can be formed on the catalyst surface, as well as formation of chemical species for activating the catalyst surface, and the oxide acts to inhibit carbon from being deposited by decomposition of the hydrocarbon-based gas <NUM> which is the source gas. Thus, while production performance for the hydrogen containing gas is enhanced, the yield of hydrogen gas in the hydrogen containing gas can be further improved and also energy efficiency can be further improved.

Hereinafter, a gas production system according to Embodiment <NUM> will be described. The configuration and the operation of the gas production system according to Embodiment <NUM> are basically the same as those in Embodiment <NUM>, while a difference is that a hydrogen sensor <NUM> is provided to the gas production device <NUM> and a second hydrogen sensor <NUM> is provided to the second gas production device <NUM>.

In the gas production system according to Embodiment <NUM>, the hydrogen sensor <NUM> provided to the gas production device <NUM> measures information, e.g., the concentration, about the yield of hydrogen gas in the hydrogen containing gas <NUM> produced by the gas production device <NUM>. In addition, the second hydrogen sensor <NUM> provided to the second gas production device <NUM> measures information, e.g., the concentration, about the yield of hydrogen gas in the hydrogen containing gas <NUM> produced by the second gas production device <NUM>. Then, the yields of hydrogen gases in the hydrogen containing gases <NUM>, <NUM> are calculated from the measured values of the hydrogen sensors <NUM>, <NUM>.

When reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM> is detected by the hydrogen sensor <NUM>, the gas ratio change means <NUM> performs correction so as to increase the time CT1 for supplying the hydrocarbon-based gas <NUM> to the gas production device <NUM> in a supply amount smaller than the reference supply amount. Alternatively, when reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM> is detected by the hydrogen sensor <NUM>, supply of the hydrocarbon-based gas <NUM> to the gas production device <NUM> is completely stopped for a certain period. After the certain period has elapsed, supply of the hydrocarbon-based gas <NUM> to the gas production device <NUM> is restarted. The stop period may be determined in advance on the basis of experience values and the like. Further, depending on the condition of the yield of hydrogen gas after supply of the hydrocarbon-based gas <NUM> is restarted, for example, if recovery of the yield is slow, the stop period may be changed as appropriate, e.g., may be set to be longer.

Similarly, when reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM> is detected by the second hydrogen sensor <NUM>, the second gas ratio change means <NUM> performs correction so as to increase the time CT2 for supplying the hydrocarbon-based gas <NUM> to the second gas production device <NUM> in a supply amount smaller than the reference supply amount. Alternatively, when reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM> is detected by the second hydrogen sensor <NUM>, supply of the hydrocarbon-based gas <NUM> to the second gas production device <NUM> is completely stopped for a certain period. After the certain period has elapsed, supply of the hydrocarbon-based gas <NUM> to the second gas production device <NUM> is restarted.

The hydrogen sensor <NUM> and the second hydrogen sensor <NUM> are not particularly limited as long as information about the yield of hydrogen gas can be measured. For example, a known measurement device or analysis device such as a quadrupole mass analyzer or a gas chromatography may be used. However, it is preferable that information about the yield of hydrogen gas can be continuously measured online, and therefore it is preferable to use a quadrupole mass analyzer.

With the system operated as described above, the time for supplying the hydrocarbon-based gas <NUM> in a supply amount smaller than the reference supply amount is appropriately ensured, and thus it is possible to stably maintain the effect of promoting formation of chemical species on the catalyst surface and the effect of forming an oxide on the catalyst surface to inhibit deposition of carbon on the catalyst surface. Thus, it is possible to stably obtain the effect of improving the yield of hydrogen gas in the hydrogen containing gas and energy efficiency while enhancing production performance for the hydrogen containing gas.

In addition, the gas production system according to Embodiment <NUM> is provided with the hydrogen sensor <NUM> capable of detecting reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM>, and the second hydrogen sensor <NUM> capable of detecting reduction in the yield of hydrogen gas in the hydrogen containing gas <NUM>.

Therefore, the time CT1 for supplying the hydrocarbon-based gas <NUM> to the gas production device <NUM> in a supply amount smaller than the reference supply amount, and the time CT2 for supplying the hydrocarbon-based gas <NUM> to the second gas production device <NUM> in a supply amount smaller than the reference supply amount, can be increased in accordance with reduction in the yield of hydrogen gas.

In this way, the time for supplying the hydrocarbon-based gas <NUM> in a supply amount smaller than the reference supply amount is appropriately ensured, and thus it is possible to stably maintain the effect of promoting formation of chemical species on the catalyst surface and the effect of forming an oxide on the catalyst surface to inhibit deposition of carbon on the catalyst surface. Thus, it is possible to stably obtain the effect of improving the yield of hydrogen gas in the hydrogen containing gas and energy efficiency while enhancing production performance for the hydrogen containing gas.

In the above, it has been described that, while the supply amount of the oxidant gas <NUM> is kept constant, the supply amount of the source gas <NUM> or the hydrocarbon-based gas <NUM> is decreased, whereby the oxidant gas <NUM> is made abundant as compared to the source gas <NUM> or the hydrocarbon-based gas <NUM>.

Claim 1:
A gas production system which is configured to apply plasma to a catalyst in a reactor (<NUM>) and reform a supplied source gas (<NUM>, <NUM>) and a supplied oxidant gas (<NUM>) to produce a product gas (<NUM>, <NUM>, <NUM>, <NUM>),
the gas production system comprising:
- source gas supply means (<NUM>) for supplying the source gas (<NUM>, <NUM>) to the reactor (<NUM>);
- oxidant gas supply means (<NUM>) for supplying the oxidant gas (<NUM>) to the reactor (<NUM>);
- gas ratio change means (<NUM>, <NUM>) for changing a ratio between a supply amount of the source gas (<NUM>, <NUM>) to be supplied to the reactor (<NUM>) by the source gas supply means (<NUM>) and a supply amount of the oxidant gas (<NUM>) to be supplied to the reactor (<NUM>) by the oxidant gas supply means (<NUM>), to make a state in which the oxidant gas (<NUM>) is abundant as compared to the source gas (<NUM>, <NUM>); and plasma generation means (<NUM>, <NUM>, <NUM>, <NUM>) for generating the plasma to be applied to the catalyst,
the gas production system further comprising:
- a gas production device (<NUM>, <NUM>) having the reactor (<NUM>), a first electrode (<NUM>) and a second electrode (<NUM>) for generating the plasma therebetween, and a catalyst layer (<NUM>) provided in the reactor (<NUM>) and containing the catalyst; and
- an external power supply (<NUM>) which is connected to the first electrode (<NUM>) and the second electrode (<NUM>) and generates voltage (<NUM>, <NUM>),
wherein the plasma is generated in the reactor (<NUM>) by the voltage generated by the external power supply (<NUM>, <NUM>) and applied between the first electrode (<NUM>) and the second electrode (<NUM>),
wherein the catalyst layer (<NUM>) is provided in the space between the first electrode (<NUM>) and the second electrode (<NUM>).