US20130068627A1

US20130068627A1 - Gas generation device and gas generation method

Info

Publication number: US20130068627A1
Application number: US13/641,294
Authority: US
Inventors: Yoshio Shodai; Osamu Yoshimoto; Noriyuki Tanaka; Yasuhiro Yano
Original assignee: Toyo Tanso Co Ltd
Current assignee: Toyo Tanso Co Ltd
Priority date: 2010-04-14
Filing date: 2011-03-23
Publication date: 2013-03-21
Also published as: WO2011129057A1; CN102834549B; EP2559790A1; KR20130040817A; JP5567375B2; CN102834549A; JP2011219847A

Abstract

A control device receives an output signal from a liquid level sensor disposed in an anode chamber. This output signal indicates whether the liquid level of the electrolytic bath in the anode chamber is higher than a reference level. When the liquid level of the electrolytic bath in the anode chamber is higher than the reference level, the control device increases, by a prescribe value, the frequency of a compressor driving voltage that is generated in an inverter circuit. This increases the rotational speed of a motor in the compressor, increases the discharge pressure of hydrogen gas being discharged from the compressor, and decreases the pressure inside the cathode chamber. As a result, the liquid level of the electrolytic bath in the cathode chamber rises, and the liquid level of the electrolytic bath in the anode chamber falls below the reference level.

Description

TECHNICAL FIELD

The present invention relates to a gas generation device and a gas generation method for generating a gas.

BACKGROUND ART

Conventionally, fluorine gas is used in the semiconductor manufacturing process and so on for material cleaning, surface modification, and other purposes. While the fluorine gas itself is used in some cases, a variety of fluorine-based gases synthesized based on the fluorine gas, such as NF₃(nitrogen trifluoride) gas, NeF (neon fluoride) gas, and ArF (argon fluoride) gas, may also be used in other cases.
For supplying fluorine gas stably in such sites, a fluorine gas generation device that generates fluorine gas by electrolysis of HF (hydrogen fluoride), for example, is used.
The fluorine gas generation device disclosed in Patent Document 1 includes an electrolyzer. The interior of the electrolyzer is divided by a partition wall into a cathode chamber and an anode chamber. In the electrolyzer, an electrolytic bath is formed with a KF-HF-based mixed molten salt. A cathode is disposed in the cathode chamber, and an anode is disposed in the anode chamber. HF is supplied through an HF supply line to the electrolytic bath in the electrolyzer for electrolysis of HF, whereby hydrogen gas is generated from the cathode and fluorine gas is generated from the anode in the electrolyzer.
At the top of the cathode chamber, an outlet for hydrogen gas is provided. The hydrogen gas generated in the cathode chamber exits from the outlet and is discharged through a hydrogen gas line on the cathode side. The hydrogen gas line is provided with an automatic valve and an HF adsorption column. Further, at the top of the cathode chamber, a purge gas inlet/outlet for supplying an inert gas into the cathode chamber is provided. This allows the inert gas to be supplied into the cathode chamber from an inert gas line through the purge gas inlet/outlet. The inert gas line is also provided with an automatic valve.
At the top of the anode chamber, an outlet for fluorine gas is provided. The fluorine gas generated in the anode chamber exits from the outlet and is discharged through a fluorine gas line. The fluorine gas line is provided with an HF adsorption column and an automatic valve. Furthermore, on the fluorine gas line, a compressor unit is provided on the downstream of the HF adsorption column and the automatic valve. Further, at the top of the anode chamber, a purge gas inlet/outlet for supplying an inert gas into the anode chamber is provided. This allows the inert gas to be supplied also into the anode chamber from an inert gas line through the purge gas inlet/outlet. This inert gas line is also provided with an automatic valve.
In each of the cathode chamber and the anode chamber, a liquid level sensor is provided which detects the liquid level of the electrolytic bath in the corresponding chamber. The automatic valves disposed on the hydrogen gas line, the fluorine gas line, and the inert gas lines open/close in accordance with the liquid levels of the electrolytic bath in the respective chambers detected by the liquid level sensors. As the automatic valves open/close in response to the liquid levels detected by the liquid level sensors, fluctuations in liquid level of the electrolytic bath are restricted, and accordingly, fluctuations in electrolysis conditions upon electrolysis of HF are restricted.

[Patent Document 1] JP 2004-52105 A

SUMMARY OF INVENTION

Technical Problem

In order to restrict the fluctuations in liquid level of the electrolytic bath, however, it is necessary to open/close the automatic valves frequently. Particularly in the case where the liquid level fluctuates constantly, the number of operations of opening/closing the automatic valves per unit time increases. In this case, the lives of the automatic valves are shortened, and the maintenance (replacement, repair, etc.) of the automatic valves needs to be performed frequently. This leads to an increase in maintenance cost.
An object of the present invention is to provide a gas generation device and a gas generation method capable of reducing the maintenance cost while restricting the fluctuations in liquid level of the electrolytic bath.

Solution to Problem

(1) According to an aspect of the present invention, a gas generation device that generates a first gas and a second gas by electrolysis includes an electrolyzer divided into a first chamber and a second chamber and containing therein an electrolytic bath including a compound to be electrolyzed, a first gas discharge path through which the first gas generated in the first chamber is discharged, a second gas discharge path through which the second gas generated in the second chamber is discharged, a liquid level detector that detects a liquid level of the electrolytic bath in the second chamber, a first pump having a motor and provided on the first gas discharge path, a first inverter circuit that generates a driving voltage to be applied to the motor of the first pump, and a controller that controls the first inverter circuit, in the case where the liquid level detected by the liquid level detector is higher than a predetermined reference level, such that at least one of an effective value and a frequency of the driving voltage being applied to the motor of the first pump increases.
In this gas generation device, electrolysis of the compound included in the electrolytic bath is carried out, so that a first gas is generated in the first chamber and a second gas is generated in the second chamber.
The first gas generated in the first chamber is discharged through the first gas discharge path by the first pump having a motor. The second gas generated in the second chamber is discharged through the second gas discharge path. The first pump operates as the driving voltage generated by the first inverter circuit is applied to the motor.
The liquid level of the electrolytic bath in the second chamber is detected by the liquid level detector. In the case where the detected liquid level is higher than a reference level, the first inverter circuit is controlled such that at least one of the effective value and frequency of the driving voltage being applied to the motor of the first pump increases.
In this case, the rotational speed of the motor of the first pump increases, and the discharge pressure of the first gas by the first pump increases, so that the pressure inside the first chamber decreases. As a result, the liquid level of the electrolytic bath in the first chamber rises, and also, the liquid level of the electrolytic bath in the second chamber is adjusted to a level not higher than the reference level. In this manner, the fluctuations in liquid level of the electrolytic bath are restricted.
Further, in the first gas discharge path, the discharge pressure of the first gas is adjusted by changing the rotational speed of the motor of the first pump. This eliminates the need to adjust the discharge pressure of the first gas through the operations of opening/closing the open/close valves. It is thus unnecessary to perform maintenance due to the early deterioration of the open/close valves, and the number of times of maintenance work decreases. This results in a reduction of the maintenance cost of the gas generation device.
(2) The gas generation device may further include a first pressure detector that detects a pressure inside the first chamber, and, in the case where the liquid level detected by the liquid level detector is not higher than the reference level, the controller may control at least one of an effective value and a frequency of the driving voltage generated by the first inverter circuit such that the pressure detected by the first pressure detector approaches a first target value.
In this case, the pressure inside the first chamber is detected by the first pressure detector. In the case where the liquid level detected by the liquid level detector is not higher than the reference level, at least one of the effective value and frequency of the driving voltage generated by the first inverter circuit is controlled such that the pressure detected by the first pressure detector approaches the first target value.
This changes the rotational speed of the motor of the first pump, and changes the discharge pressure of the first gas by the first pump, whereby the pressure inside the first chamber is adjusted to approach the first target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the first chamber, while restricting the fluctuations in liquid level in the second chamber.
(3) The gas generation device may further include a second pump having a motor and provided on the second gas discharge path, a second inverter circuit that generates a driving voltage to be applied to the motor of the second pump, and a second pressure detector that detects a pressure inside the second chamber, and the controller may control at least one of an effective value and a frequency of the driving voltage generated by the second inverter circuit such that the pressure detected by the second pressure detector approaches a second target value.
In this case, the second gas generated in the second chamber is discharged through the second gas discharge path by the second pump having a motor. The second pump operates as the driving voltage generated by the second inverter circuit is applied to the motor.
The pressure inside the second chamber is detected by the second pressure detector. At least one of the effective value and frequency of the driving voltage generated by the second inverter circuit is controlled such that the pressure detected by the second pressure detector approaches the second target value.
This changes the rotational speed of the motor of the second pump, and changes the discharge pressure of the second gas by the second pump, whereby the pressure inside the second chamber is adjusted to approach the second target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the second chamber, while restricting the fluctuations in liquid level in the second chamber.
(4) The gas generation device may further include a first pressure detector that detects a pressure inside the first chamber, a second pump having a motor and provided on the second gas discharge path, a second inverter circuit that generates a driving voltage to be applied to the motor of the second pump, and a second pressure detector that detects a pressure inside the second chamber, and, in the case where the liquid level detected by the liquid level detector is not higher than the reference level, the controller may control at least one of an effective value and a frequency of the driving voltage generated by the first inverter circuit such that the pressure detected by the first pressure detector approaches a first target value, and may also control at least one of an effective value and a frequency of the driving voltage generated by the second inverter circuit such that the pressure detected by the second pressure detector approaches a second target value that is smaller than the first target value.
In this case, the pressure inside the first chamber is detected by the first pressure detector. In the case where the liquid level detected by the liquid level detector is not higher than the reference level, at least one of the effective value and frequency of the driving voltage generated by the first inverter circuit is controlled such that the pressure detected by the first pressure detector approaches the first target value.
This changes the rotational speed of the motor of the first pump, and changes the discharge pressure of the first gas by the first pump, whereby the pressure inside the first chamber is adjusted to approach the first target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the first chamber, while restricting the fluctuations in liquid level in the second chamber.
Further, the second gas generated in the second chamber is discharged through the second gas discharge path by the second pump having a motor. The second pump operates as the driving voltage generated by the second inverter circuit is applied to the motor.
The pressure inside the second chamber is detected by the second pressure detector. At least one of the effective value and frequency of the driving voltage generated by the second inverter circuit is controlled such that the pressure detected by the second pressure detector approaches the second target value.
This changes the rotational speed of the motor of the second pump, and changes the discharge pressure of the second gas by the second pump, whereby the pressure inside the second chamber is adjusted to approach the second target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the second chamber, while restricting the fluctuations in liquid level in the second chamber.
The second target value is smaller than the first target value. In this case, the pressures inside the first and second chambers are adjusted to approach the first and second target values, respectively, and accordingly, the pressure inside the second chamber becomes lower than the pressure inside the first chamber. This prevents the liquid level of the electrolytic bath in the first chamber from rising beyond the liquid level of the electrolytic bath in the second chamber.
(5) The gas generation device may further include a first open/close valve provided on the first gas discharge path, and a second open/close valve provided on the second gas discharge path, and the controller may open the first and second open/close valves in the case where electrolysis is carried out in the electrolyzer, and may close the first and second open/close valves in the case where no electrolysis is carried out in the electrolyzer.
In this case, the first and second open/close valves are opened when electrolysis takes place in the electrolyzer, while the first and second open/close valves are closed when no electrolysis takes place in the electrolyzer.
This allows the first gas generated in the first chamber to be discharged through the first gas discharge path when electrolysis is carried out in the electrolyzer. This also allows the second gas generated in the second chamber to be discharged through the second gas discharge path.
On the other hand, when no electrolysis is carried out in the electrolyzer, the atmosphere outside the gas generation device is prevented from flowing into the first chamber through the first gas discharge path. And the atmosphere outside the gas generation device is prevented from flowing into the second chamber through the second gas discharge path.
(6) The first chamber may be a cathode chamber, and the second chamber may be an anode chamber.
In this case, the liquid level of the electrolytic bath in the anode chamber is detected by the liquid level detector. In the case where the detected liquid level is higher than the reference level, the first inverter circuit is controlled such that at least one of the effective value and frequency of the driving voltage being applied to the motor of the first pump increases.
This increases the rotational speed of the motor of the first pump, and increases the discharge pressure of the first gas by the first pump, whereby the pressure inside the anode chamber decreases. As a result, the liquid level of the electrolytic bath in the anode chamber rises, and also, the liquid level of the electrolytic bath in the cathode chamber is adjusted to a level not higher than the reference level.
(7) The second gas may be fluorine. In the second chamber where fluorine is generated, the liquid level of the electrolytic bath is likely to rise at the time of electrolysis of the compound. Even in such a case, the fluctuations in liquid level of the electrolytic bath in the second chamber are restricted, which ensures a stable supply of fluorine.
(8) According to another aspect of the present invention, a gas generation method for generating a first gas and a second gas by electrolysis by using an electrolyzer divided into a first chamber and a second chamber includes the steps of generating the first and second gases in the first and second chambers, respectively, by applying a voltage to an electrolytic bath contained in the electrolyzer, and discharging the first and second gases generated in the first and second chambers through first and second gas discharge paths, respectively, controlling, by a first pump having a motor, the discharge of the first gas through the first gas discharge path, detecting a liquid level of the electrolytic bath in the second chamber, applying a driving voltage to the motor of the first pump by a first inverter circuit, and in the case where the detected liquid level is higher than a predetermined reference level, controlling the first inverter circuit such that at least one of an effective value and a frequency of the driving voltage being applied to the motor of the first pump increases.
In this gas generation method, a voltage is applied to the electrolytic bath contained in the electrolyzer, so that a first gas is generated in the first chamber and a second gas is generated in the second chamber. The first and second gases generated in the first and second chambers are discharged through the first and second gas discharge paths, respectively. The discharge of the first gas through the first gas discharge path is controlled by the first pump having a motor. The first pump operates as a driving voltage is applied to the motor by the first inverter circuit.
The liquid level of the electrolytic bath in the second chamber is detected. In the case where the detected liquid level is higher than a reference level, the first inverter circuit is controlled such that at least one of the effective value and frequency of the driving voltage being applied to the motor of the first pump increases.
In this case, the rotational speed of the motor of the first pump increases, and the discharge pressure of the first gas by the first pump increases, so that the pressure inside the first chamber decreases. As a result, the liquid level of the electrolytic bath in the first chamber rises, and also, the liquid level of the electrolytic bath in the second chamber is adjusted to a level not higher than the reference level. In this manner, the fluctuations in liquid level of the electrolytic bath are restricted.
Further, in the first gas discharge path, the discharge pressure of the first gas is adjusted by changing the rotational speed of the motor of the first pump. This eliminates the need to adjust the discharge pressure of the first gas through the operations of opening/closing the open/close valves. It is thus unnecessary to perform maintenance due to the early deterioration of the open/close valves, and the number of times of maintenance work decreases. This results in a reduction of the maintenance cost of the gas generation device.
(9) The gas generation method may further include the steps of detecting a pressure inside the first chamber, in the case where the detected liquid level is not higher than the predetermined reference level, controlling at least one of an effective value and a frequency of the driving voltage generated by the first inverter circuit such that the detected pressure inside the first chamber approaches a first target value, controlling, by a second pump having a motor, the discharge of the second gas through the second gas discharge path, applying a driving voltage to the motor of the second pump by a second inverter circuit, detecting a pressure inside the second chamber, and controlling at least one of an effective value and a frequency of the driving voltage generated by the second inverter circuit such that the detected pressure inside the second chamber approaches a second target value that is smaller than the first target value.
In this case, the pressure inside the first chamber is detected. In the case where the detected liquid level is not higher than the reference level, at least one of the effective value and frequency of the driving voltage generated by the first inverter circuit is controlled such that the detected pressure approaches the first target value.
This changes the rotational speed of the motor of the first pump, and changes the discharge pressure of the first gas by the first pump, whereby the pressure inside the first chamber is adjusted to approach the first target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the first chamber, while restricting the fluctuations in liquid level in the second chamber.
The second gas generated in the second chamber is discharged through the second gas discharge path by the second pump having a motor. The second pump operates as the driving voltage generated by the second inverter circuit is applied to the motor.
The pressure inside the second chamber is detected. At least one of the effective value and frequency of the driving voltage generated by the second inverter circuit is controlled such that the detected pressure approaches the second target value.
This changes the rotational speed of the motor of the second pump, and changes the discharge pressure of the second gas by the second pump, whereby the pressure inside the second chamber is adjusted to approach the second target value. Accordingly, it is possible to restrict the fluctuations in pressure inside the second chamber, while restricting the fluctuations in liquid level in the second chamber.
The second target value is smaller than the first target value. In this case, the pressures inside the first and second chambers are adjusted to approach the first and second target values, respectively, and accordingly, the pressure inside the second chamber becomes lower than the pressure inside the first chamber. This prevents the liquid level of the electrolytic bath in the first chamber from rising beyond the liquid level of the electrolytic bath in the second chamber.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce the maintenance cost while restricting the fluctuations in liquid level of the electrolytic bath.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of a fluorine gas generation device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a part of a control system in the fluorine gas generation device in FIG. 1.

FIG. 3 shows graphs illustrating specific examples of liquid level control and pressure control.

FIG. 4 is a flowchart illustrating a series of processes of electrolysis using the liquid level control and the pressure control.

FIG. 5 is a flowchart illustrating a series of processes of electrolysis using the liquid level control and the pressure control.

FIG. 6 is a schematic diagram showing the configuration of the fluorine gas generation device according to another embodiment.

FIG. 7 is a schematic diagram showing the configuration of the fluorine gas generation device according to yet another embodiment.

DESCRIPTION OF EMBODIMENTS

A gas generation device and a gas generation method according to an embodiment of the present invention will now be described with reference to the drawings. In the following embodiment, a fluorine gas generation device for generating fluorine gas will be described as an example of the gas generation device.

(1) Configuration of the Fluorine Gas Generation Device

FIG. 1 is a schematic diagram showing the configuration of the fluorine gas generation device according to an embodiment of the present invention. As shown in FIG. 1, the fluorine gas generation device 100 includes an electrolyzer 1. The electrolyzer 1 is formed, for example, of Ni (nickel), Monel, pure iron, stainless steel, or other metal or alloy. The interior of the electrolyzer 1 is divided by a partition wall 2 into a cathode chamber 3 and an anode chamber 4. The partition wall 2 is made of Ni or Monel, for example.
In the electrolyzer 1, an electrolytic bath 5 of KF-HF-based mixed molten salt is formed. A cathode 6 of Ni (nickel), for example, is disposed in the cathode chamber 3, and an anode 7 of carbon with low polarizability, for example, is disposed in the anode chamber 4. As HF (hydrogen fluoride) is supplied through an HF supply pipe 10 to the electrolytic bath 5 in the electrolyzer 1, electrolysis of HF takes place. As a result, in the electrolyzer 1, hydrogen gas is primarily generated from the cathode 6 and fluorine gas is primarily generated from the anode 7.
At the top of the cathode chamber 3, a cathode outlet 20 a is provided. Connected to the cathode outlet 20 a is an (upstream) end of a hydrogen gas discharge pipe 20. The hydrogen gas generated in the cathode chamber 3 exits from the cathode outlet 20 a and is discharged through the hydrogen gas discharge pipe 20. The hydrogen gas discharge pipe 20 has an HF adsorption column 24, a control valve 21, a compressor 22, and a control valve 23 provided in this order from the upstream to the downstream.
The HF adsorption column 24 is packed with NaF or the like. The HF adsorption column 24 serves to adsorb HF within a mixture of HF and hydrogen gas that is discharged from the cathode chamber 3. The compressor 22 is connected with an inverter circuit 22I. A driving voltage generated by the inverter circuit 22I is applied to the compressor 22.
The hydrogen gas discharge pipe 20 has its downstream end connected, for example, to an exhaust line in a factory. This allows the hydrogen gas discharged from the cathode chamber 3 to be discharged through the factory exhaust line.
At the top of the anode chamber 4, an anode outlet 30 a is provided. Connected to the anode outlet 30 a is an (upstream) end of a fluorine gas discharge pipe 30. The fluorine gas generated in the anode chamber 4 exits from the anode outlet 30 a and is discharged through the fluorine gas discharge pipe 30. The fluorine gas discharge pipe 30 has an HF adsorption column 34, a control valve 31, a compressor 32, and a control valve 33 provided in this order from the upstream to the downstream.
The HF adsorption column 34 is packed with NaF or the like. The HF adsorption column 34 serves to adsorb HF within a mixture of HF and fluorine gas that is discharged from the anode chamber 4. The compressor 32 is connected with an inverter circuit 32I. A driving voltage generated by the inverter circuit 32I is applied to the compressor 32.
The fluorine gas discharge pipe 30 has its downstream end connected, for example, to a manufacturing line in a factory. This allows the fluorine gas discharged from the anode chamber 4 to be supplied, at a predetermined flow rate, to the factory manufacturing line or the like.
The cathode chamber 3 is provided with a pressure gauge PS1 that measures the pressure inside the cathode chamber 3. The anode chamber 4 is provided with a pressure gauge PS2 that measures the pressure inside the anode chamber 4. The anode chamber 4 is further provided with a liquid level sensor 40 that detects the liquid level of the electrolytic bath 5 in the anode chamber 4.
The HF supply pipe 10 is provided with an automatic valve 11 and an orifice 12. In order to prevent the electrolytic bath 5 from being sucked into the HF supply pipe 10, a control valve 13 is connected between the hydrogen gas discharge pipe 20 and the HF supply pipe 10 on the downstream of the orifice 12. It is noted that the HF supply pipe 10 is provided with a pressure gauge (not shown).
In the present embodiment, the compressors 22, 32 are bellows compressors that respectively include metal bellows and motors 22M, 23M (FIG. 2), which will be described later. During the operations of the compressors 22, 32, the metal bellows are expanded/contracted by the motors 22M, 23M. The amounts of expansion/contraction as well as the cycles of expansion and contraction of the respective bellows at that time can be adjusted so as to adjust the discharge pressures of the gases (hydrogen gas and fluorine gas) by the compressors 22, 23. It is noted that the amount of expansion/contraction of the bellows refers to the difference between the length of the bellows in the most expanded state and the length of the bellows in the most contracted state.

(2) Control System in the Fluorine Gas Generation Device

A control device 90 includes a central processing unit (CPU) and a memory, or a microcomputer. The control device 90 controls the operations of the elements constituting the fluorine gas generation device 100.
FIG. 2 is a block diagram showing a part of a control system in the fluorine gas generation device 100 in FIG. 1. As shown in FIG. 2, the control device 90 receives an output signal from the liquid level sensor 40 disposed in the anode chamber 4. This output signal indicates whether the liquid level of the electrolytic bath 5 in the anode chamber 4 is higher than a predetermined liquid level (hereinafter, referred to as the “reference level”). The control device 90 controls the inverter circuit 22I on the basis of the output signal from the liquid level sensor 40.
More specifically, in the case where the liquid level of the electrolytic bath 5 in the anode chamber 4 is higher than the reference level, the control device 90 increases the frequency of the driving voltage, generated in the inverter circuit 22I, by a prescribed value (of not less than 10 Hz and not more than 20 Hz, for example). This increases the rotational speed of the motor 22M included in the compressor 22, and shortens the cycle of expansion and contraction of the bellows, and accordingly, the discharge pressure of the hydrogen gas discharged from the compressor 22 increases, and the pressure inside the cathode chamber 3 decreases. As a result, the liquid level of the electrolytic bath 5 in the cathode chamber 3 rises, and the liquid level of the electrolytic bath 5 in the anode chamber 4 falls below the reference level.
On the other hand, in the case where the liquid level of the electrolytic bath 5 in the anode chamber 4 is not higher than the reference level, the control device 90 refrains from increasing the frequency of the driving voltage of the compressor 22, generated in the inverter circuit 22I, by the prescribed value described above.
In this manner, when the liquid level of the electrolytic bath 5 in the anode chamber 4 rises beyond the reference level, the control device 90 controls the inverter circuit 22I such that the liquid level falls to the reference level or below.
In the following description, the control of the inverter circuit 22I based on the output signal from the liquid level sensor 40 performed by the control device 90 will be referred to as “liquid level control.”
While the description was made above about the case where the liquid level control is performed by changing the frequency of the driving voltage generated in the inverter circuit 22I, the liquid level control may be performed by changing an effective value of the driving voltage generated in the inverter circuit 22I. In this case, the discharge pressure of the hydrogen gas discharged from the compressor 22 is controlled in accordance with a change in the amount of expansion/contraction of the bellows, whereby the pressure inside the cathode chamber 3 is changed. As a result, the liquid level of the electrolytic bath 5 in the cathode chamber 3 changes, and the liquid level in the anode chamber 4 is adjusted.
The liquid level control may also be performed by changing both of the effective value and frequency of the driving voltage generated in the inverter circuit 22I. As the amount of expansion/contraction and the cycle of expansion and contraction of the bellows change, the discharge pressure of the hydrogen gas discharged from the compressor 22 is controlled, so that the pressure inside the cathode chamber 3 is changed. As a result, the liquid level of the electrolytic bath 5 in the cathode chamber 3 changes, and the liquid level in the anode chamber 4 is adjusted.
The control device 90 also receives an output signal from the pressure gauge PS1 disposed in the cathode chamber 3. The control device 90 controls at least one of the effective value and frequency of the driving voltage generated in the inverter circuit 22I on the basis of the output signal from the pressure gauge PS1. As a result, the pressure inside the cathode chamber 3 is adjusted.
For example, in the case where the value of the pressure inside the cathode chamber 3 (hereinafter, referred to as the “cathode chamber pressure value”) measured by the pressure gauge PS1 at the time of electrolysis of HF does not agree with a prescribed value (target pressure value), the control device 90 controls the inverter circuit 22I such that the difference between the cathode chamber pressure value and the target pressure value decreases. It is noted that the target pressure value is set, for example, to 100 kPa in absolute pressure.
Furthermore, the control device 90 receives an output signal from the pressure gauge PS2 disposed in the anode chamber 4. The control device 90 controls at least one of an effective value and a frequency of the driving voltage generated in the inverter circuit 32I on the basis of the output signal from the pressure gauge PS2. As a result, the pressure inside the anode chamber 4 is adjusted.
For example, in the case where the value of the pressure inside the anode chamber 4 (hereinafter, referred to as the “anode chamber pressure value”) measured by the pressure gauge PS2 at the time of electrolysis of HF does not agree with a prescribed value (target pressure value), the control device 90 controls the inverter circuit 32I such that the difference between the anode chamber pressure value and the target pressure value decreases. It is noted that the target pressure value is set, for example, to 100 kPa in absolute pressure.
In the following description, the control of the inverter circuits 22I, 32I based on the output signals from the pressure gauges PS1, PS2 performed by the control device 90 will be referred to as “pressure control.”
The control device 90 opens the control valves 21, 23, 31, 33 while electrolysis of HF is taking place, whereas the control device 90 closes the control valves 21, 23, 31, 33 while no electrolysis of HF is taking place. This prevents the hydrogen gas or the fluorine gas downstream of the compressor 22, 32 from being sucked into the cathode chamber 3 or the anode chamber 4 while no electrolysis of HF is taking place. The control device 90 also controls the opening/closing of the control valve 13.
As described above, in this fluorine gas generation device 100, in the case where the liquid level of the electrolytic bath 5 in the anode chamber 4 becomes higher than the reference level, the inverter circuit 22I is controlled such that the liquid level falls to the reference level or below, for the following reason.
In the case of conducting electrolysis of HF in the electrolyzer 1 shown in FIG. 1, the liquid level of the electrolytic bath 5 in the anode chamber 4 is likely to rise compared to the liquid level of the electrolytic bath 5 in the cathode chamber 3. Therefore, in the present embodiment, the inverter circuit 22I is controlled on the basis of the output signal from the liquid level sensor 40 such that, when the liquid level of the electrolytic bath 5 in the anode chamber 4 has risen beyond the reference level, the liquid level is adjusted to fall to the reference level or below, for restricting the fluctuations in liquid level.
In the liquid level control, the inverter circuit 22I is controlled, for the following reason.
As previously described, in the fluorine gas generation device 100 in FIG. 1, the fluorine gas discharged from the anode chamber 4 is supplied through the fluorine gas discharge pipe 30 to the manufacturing line in a factory or the like at a predetermined flow rate. Therefore, it is preferable that the discharge pressure of the fluorine gas discharged from the compressor 32 is maintained approximately constant.
Therefore, in the present embodiment, the inverter circuit 22I is controlled so as to change the discharge pressure of the compressor 22 disposed on the hydrogen gas discharge pipe 20. This allows the liquid level of the electrolytic bath 5 in the anode chamber 4 to be adjusted to the reference level or below, without causing large fluctuations in the flow rate of the fluorine gas discharged from the fluorine gas discharge pipe 30.

(3) Specific Examples of Liquid Level Control and Pressure Control

FIG. 3 shows graphs illustrating specific examples of the liquid level control and the pressure control. FIG. 3( a) shows the rotational speeds of the motors 22M, 32M when the liquid level control and the pressure control are carried out. In FIG. 3( a), the vertical axis represents rotational speed, and the horizontal axis represents time. Further, the bold solid line represents the rotational speed of the motor 22M, and the long dashed dotted line represents the rotational speed of the motor 32M.
Further, FIG. 3( b) shows the cathode chamber pressure value and the anode chamber pressure value when the liquid level control and the pressure control are carried out. In FIG. 3( b), the vertical axis represents pressure, and the horizontal axis represents time. Further, the bold broken line represents the cathode chamber pressure value, and the solid line represents the anode chamber pressure value.
At time t0, electrolysis of HF is initiated, with the liquid level of the electrolytic bath 5 in the anode chamber 4 being not higher than the reference level. In the case where the liquid level of the electrolytic bath 5 is maintained at the reference level or below from time t0 to time t1, the control device 90 controls the inverter circuits 22I, 32I on the basis of the output signals from the pressure gauges PS1, PS2 (FIG. 1) (pressure control).
As such, as shown in FIG. 3( a), during the period PP in which the liquid level of the electrolytic bath 5 is not higher than the reference level, the inverter circuits 22I, 32I are controlled in accordance with the fluctuations of the cathode chamber pressure value and the anode chamber pressure value, which results in gradual changes of the rotational speeds of the motors 22M, 32M. In this manner, the pressure inside the cathode chamber 3 and the pressure inside the anode chamber 4 are both adjusted to approach a target pressure value U.
In the case where the liquid level of the electrolytic bath 5 continues to be higher than the reference level from time t1 to time t2, during this period LP, the frequency of the driving voltage of the compressor 22, generated in the inverter circuit 22I, is maintained at a value increased by a prescribed value T with respect to the frequency at time t1 (liquid level control). This causes the liquid level of the electrolytic bath 5 to be adjusted to fall to the reference level or below. It is noted that the prescribed value T is set to the order of not less than 5 Hz and not more than 15 Hz, for example.
At time t2, when the liquid level of the electrolytic bath 5 falls to the reference level or below, the frequency of the driving voltage, generated in the inverter circuit 22I, is decreased by the prescribed value T with respect to the frequency at that time t2. As a result, as shown in FIG. 3( a), the rotational speed of the motor 22M steeply drops by the prescribed value T from time t2, so that it becomes approximately the same as the rotational speed at the start point (time t1) of that period LP.
In the example shown in FIG. 3, after the time t2, the liquid level becomes higher than the reference level during the periods from time t3 to time t4, from time t5 to time t6, and from time t7 to time t8. In each of these periods LP as well, the frequency of the driving voltage generated in the inverter circuit 22I is maintained at a level increased by the prescribed value T with respect to the frequency at the start point (time t3, t5, t7) of each period LP (liquid level control). In this manner, the liquid level of the electrolytic bath 5 is adjusted to fall to the reference level or below.
It is noted that during the periods LP described above, the control device 90 continues to control the inverter circuit 32I on the basis of the output signals from the pressure gauge PS2 (FIG. 1) (pressure control). Thus, as shown in FIG. 3( a), the rotational speed of the motor 32M shows gradual changes during the periods LP as well.
As in the period PP from time t0 to time t1, in each of the periods PP from time t2 to time t3, from time t4 to time t5, and from time t6 to time t7 where the liquid level of the electrolytic bath 5 in the anode chamber 4 is not higher than the reference level, the inverter circuits 22I, 32I are controlled in accordance with the fluctuations of the cathode chamber pressure value and the anode chamber pressure value. As a result, as shown in FIG. 3( b), in each period PP, the cathode chamber pressure value gradually approaches the target pressure value U, and the anode chamber pressure value also gradually approaches the target pressure value U.
As described above, by the liquid level control and the pressure control performed by the control device 90, the fluctuations in liquid level of the electrolytic bath 5 are restricted and, at the same time, the fluctuations in pressure inside the cathode chamber 3 and the anode chamber 4 are restricted.

(4) Control Flow

FIGS. 4 and 5 show a flowchart illustrating a series of processes of electrolysis using the liquid level control and the pressure control. In the following, the control of the inverter circuit 22I by the control device 90 will be described. In the initial state, the compressors 22, 32 are operating at prescribed rotational speeds in advance.
First, when the start of electrolysis of HF is instructed by an input device (not shown) or the like, the control device 90 applies a prescribed voltage across the cathode 6 and the anode 7 (step S1), and opens two control valves 21, 23 disposed on the hydrogen gas discharge pipe 20 (step S2).
Next, the control device 90 determines, on the basis of the output signal from the liquid level sensor 40, whether the liquid level of the electrolytic bath 5 in the anode chamber 4 is higher than a reference level (step S3).
If the liquid level is higher than the reference level, the control device 90 controls the inverter circuit 22I to increase the rotational speed of the motor 22M by a prescribed value T (step S4). For example, the control device 90 increases the frequency of the driving voltage of the compressor 22, generated in the inverter circuit 22I, by a prescribed value from the current frequency, to thereby increase the rotational speed of the motor 22M by the prescribed value T.
The control device 90 then determines, on the basis of the output signal from the liquid level sensor 40, whether the liquid level of the electrolytic bath 5 in the anode chamber 4 is higher than the reference level (step S5). This step is repeated until the liquid level falls to the reference level or below. Thereafter, when the liquid level becomes not higher than the reference level, the control device 90 controls the inverter circuit 22I to decrease the rotational speed of the motor 22M by the prescribed value T (step S6). The process then returns to step S3.
If it is determined in step S3 that the liquid level is not higher than the reference level, the control device 90 acquires a cathode chamber pressure value measured by the pressure gauge PS1 (step S7).
Here, in the control device 90, a target pressure value U for the cathode chamber 3 is stored in advance. The target pressure value U is set, for example, by an operator through manipulation of an input device or the like.
The control device 90 determines whether the acquired cathode chamber pressure value agrees with the preset target pressure value U (step S8).
If the cathode chamber pressure value agrees with the target pressure value U, the control device 90 controls the inverter circuit 22I in FIG. 2 to maintain the rotational speed of the motor 22M at the current value (step S9). For example, the control device 90 maintains the frequency of the driving voltage generated in the inverter circuit 22I at the current value, to thereby maintain the rotational speed of the motor 22M.
If the cathode chamber pressure value does not agree with the target pressure value U, the control device 90 changes the rotational speed of the motor 22M by controlling the inverter circuit 22I such that the difference between the cathode chamber pressure value and the target pressure value U decreases (step S10). For example, the control device 90 changes the frequency of the driving voltage generated in the inverter circuit 22I from the current value such that the difference between the cathode chamber pressure value and the target pressure value U decreases, to thereby change the rotational speed of the motor 22M.
For example, in the case where the cathode chamber pressure value is lower than the target pressure value U, the control device 90 controls the inverter circuit 22I such that the driving voltage applied to the motor 22M decreases. This reduces the rotational speed of the motor 22M, and decreases the discharge pressure of the compressor 22. As a result, the cathode chamber pressure value increases to approach the target pressure value U, whereby the difference between the cathode chamber pressure value and the target pressure value U decreases.
Conversely, in the case where the cathode chamber pressure value is higher than the target pressure value U, the control device 90 controls the inverter circuit 22I such that the driving voltage applied to the motor 22M increases. This increases the rotational speed of the motor 22M, and increases the discharge pressure of the compressor 22. As a result, the cathode chamber pressure value decreases to approach the target pressure value U, whereby the difference between the anode chamber pressure value and the target pressure value U decreases.
After the processing in step S9 or S10, the control device 90 determines whether an end of the electrolysis of HF has been instructed by an input device or the like (step S11). If the end of electrolysis has not been instructed, the control device 90 returns to the processing in step S3. On the other hand, if the end of electrolysis has been instructed, the control device 90 stops applying the voltage across the cathode 6 and the anode 7 (step S12), and closes the two control valves 21, 23 disposed on the hydrogen gas discharge pipe 20 (step S13). This terminates the electrolysis of HF.
In the flowchart in FIGS. 4 and 5, the processing in steps S3 through S6 corresponds to the above-described liquid level control, and the processing in steps S7 through S10 corresponds to the above-described pressure control.
While the control of the inverter circuit 22I by the control device 90 has been described above, when the electrolysis of HF is started, the control device 90 controls the inverter circuit 32I similarly as in the above-described processing in steps S7 through S10.

(5) Effects

(5-a) In this fluorine gas generation device 100, the control device 90 carries out the liquid level control. Therefore, even when the liquid level of the electrolytic bath 5 in the anode chamber 4 becomes higher than the reference level, the liquid level is adjusted to fall to the reference level or below. The fluctuations in liquid level of the electrolytic bath 5 are restricted in this manner.
Further, the liquid level control is adjusted by changing the rotational speed of the motor 22M of the compressor 22. This eliminates the need to adjust the discharge pressure of the hydrogen gas in the hydrogen gas discharge pipe 20 through the operations of opening/closing the control valves 21, 23, 31, 33. It is thus unnecessary to perform maintenance due to the early deterioration of the control valves 21, 23, 31, 33, and the number of times of maintenance work decreases. This results in a reduction of the maintenance cost of the fluorine gas generation device 100.
(5-b) Further, in this fluorine gas generation device 100, the control device 90 carries out the pressure control in addition to the liquid level control. This restricts the fluctuations in pressure inside the cathode chamber 3 and the anode chamber 4, while restricting the fluctuations in liquid level of the electrolytic bath 5. As a result, the fluctuations in electrolysis conditions upon electrolysis of HF are restricted.
(5-c) The liquid level control and the pressure control are carried out by changing the rotational speed of the motor 22M by controlling the inverter circuits 22I, 32I. Accordingly, compared to the case of opening/closing the control valves 21, 23, 31, 33, the discharge pressure of the hydrogen gas in the hydrogen gas discharge pipe 20 and the discharge pressure of the fluorine gas in the fluorine gas discharge pipe 30 can be adjusted readily and finely. Therefore, even if the electrolyzer 1 is reduced in size, the pressure in each chamber 3, 4 can be controlled with ease and with precision. This enables downsizing of the fluorine gas generation device 100.

(6) Other Embodiments

(6-a) In the above embodiment, the description was made about the case of setting a common target pressure value U for the cathode chamber pressure value and the anode chamber pressure value for performing the pressure control. Not limited thereto, the target pressure value (first target pressure value) set for the cathode chamber pressure value and the target pressure value (second target pressure value) set for the anode chamber pressure value may differ from each other. In this case, for example, the second target pressure value is preferably set smaller than the first target pressure value.
Thus, by the pressure control, the cathode chamber pressure value is adjusted to approach the first target pressure value, and the anode chamber pressure value is adjusted to approach the second target pressure value that is smaller than the first target pressure value. Consequently, the pressure inside the cathode chamber 3 becomes higher than the pressure inside the anode chamber 4. This prevents the liquid level of the electrolytic bath 5 in the cathode chamber 3 from rising beyond the liquid level of the electrolytic bath 5 in the anode chamber 4.
For example, the first target pressure value is set to 100 kPa in absolute pressure, and the second target pressure value is set to not less than 95 kPa and not more than 99 kPa in absolute pressure.
It is noted that the first and second target pressure values may be set as appropriate in accordance with the volumetric capacities of the cathode chamber 3 and the anode chamber 4.
(6-b) As described above, in the fluorine gas generation device 100 in FIG. 1, the liquid level sensor 40 for detecting the liquid level of the electrolytic bath 5 is disposed in the anode chamber 4. The control device 90 carries out the liquid level control on the basis of the output signal from the liquid level sensor 40.
Not limited thereto, in the case where the flow rate of the fluorine gas discharged from the fluorine gas discharge pipe 30 is not particularly determined, the liquid level sensor 40 may be disposed in the cathode chamber 3. Further, the control device 90 may carry out the liquid level control on the basis of the output signal from the liquid level sensor 40 disposed in the cathode chamber 3.
FIG. 6 is a schematic diagram showing the configuration of the fluorine gas generation device according to another embodiment. In the following, the differences of the fluorine gas generation device 100 in FIG. 6 from the fluorine gas generation device 100 in FIG. 1 will be described.
As shown in FIG. 6, in this fluorine gas generation device 100, the liquid level sensor 40 is not disposed in the anode chamber 4, but disposed in the cathode chamber 3. In the present example, the control device 90 controls the inverter circuit 32I on the basis of the output signal from the liquid level sensor 40 (liquid level control).
For example, in the case where the liquid level of the electrolytic bath 5 in the cathode chamber 3 has become higher than the reference level, the control device 90 causes the frequency of the driving voltage generated in the inverter circuit 32I to be increased by a prescribed value with respect to the frequency at that time point. This increases the rotational speed of the motor 32M included in the compressor 32, and increases the discharge pressure of the fluorine gas discharged from the compressor 32, whereby the pressure inside the anode chamber 4 decreases. As a result, the liquid level of the electrolytic bath 5 in the anode chamber 4 rises, and also, the liquid level of the electrolytic bath 5 in the cathode chamber 3 falls below the reference level.
In this manner, even when the liquid level of the electrolytic bath 5 in the cathode chamber 3 becomes higher than the reference level, the liquid level control is carried out on the basis of the output signal from the liquid level sensor 40, so that the liquid level is adjusted to fall to the reference level or below.
(6-c) Not limited to the fluorine gas generation devices 100 in FIGS. 1 and 6, the liquid level sensor 40 may be provided in each of the cathode chamber 3 and the anode chamber 4. The control device 90 may carry out the liquid level control on the basis of the output signals from the liquid level sensors 40 disposed in the cathode chamber 3 and the anode chamber 4.
FIG. 7 is a schematic diagram showing the configuration of the fluorine gas generation device according to yet another embodiment. In the fluorine gas generation device 100 in FIG. 7, a liquid level sensor 40 is disposed in each of the cathode chamber 3 and the anode chamber 4. In the present example, the control device 90 controls the inverter circuits 22I, 32I on the basis of the output signals from the respective liquid level sensors 40 (liquid level control).
In this manner, even when the liquid level of the electrolytic bath 5 in the cathode chamber 3 becomes higher than the reference level, the liquid level is adjusted to fall to the reference level or below. Further, even when the liquid level of the electrolytic bath 5 in the anode chamber 4 becomes higher than the reference level, the liquid level is adjusted to fall to the reference level or below. It is thus possible to restrict the fluctuations in liquid level of the electrolytic bath 5 in the cathode chamber 3 and the anode chamber 4.

(7) Correspondences between the Elements Recited in the Claims and Those Described in the Embodiments

In the following paragraphs, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained.
In the embodiments described above, the hydrogen gas is an example of the first gas, the fluorine gas is an example of the second gas, the cathode chamber 3 is an example of the first chamber, the anode chamber 4 is an example of the second chamber, the hydrogen gas discharge pipe 20 is an example of the first gas discharge path, and the fluorine gas discharge pipe 30 is an example of the second gas discharge path.
Further, the liquid level sensor 40 is an example of the liquid level detector, the compressor 22 is an example of the first pump, the motor 22M is an example of the motor of the first pump, the inverter circuit 22I is an example of the first inverter circuit, and the pressure gauge PS1 is an example of the first pressure detector.
Furthermore, the compressor 32 is an example of the second pump, the motor 32M is an example of the motor of the second pump, the inverter circuit 32I is an example of the second inverter circuit, and the pressure gauge PS2 is an example of the second pressure detector.
Further, the control device 90 is an example of the controller, the control valves 21, 23 are examples of the first open/close valve, and the control valves 31, 34 are examples of the second open/close valve.
Furthermore, the target pressure value U is an example of the first and second target values, the first target pressure value is an example of the first target value, and the second target pressure value is an example of the second target value.
As the elements recited in the claims, a variety of other elements having the configuration or function recited in the claims may be used as well.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the generation of gases by electrolysis.

Claims

1. A gas generation device that generates a first gas and a second gas by electrolysis, comprising:

an electrolyzer divided into a first chamber and a second chamber and containing therein an electrolytic bath including a compound to be electrolyzed;

a first gas discharge path through which the first gas generated in said first chamber is discharged;

a second gas discharge path through which the second gas generated in said second chamber is discharged;

a liquid level detector that detects a liquid level of the electrolytic bath in said second chamber;

a first pump having a motor and provided on said first gas discharge path;

a first inverter circuit that generates a driving voltage to be applied to the motor of said first pump; and

a controller that controls said first inverter circuit, in the case where the liquid level detected by said liquid level detector is higher than a predetermined reference level, such that at least one of an effective value and a frequency of the driving voltage being applied to the motor of said first pump increases.

2. The gas generation device according to claim 1, further comprising a first pressure detector that detects a pressure inside said first chamber, wherein

in the case where the liquid level detected by said liquid level detector is not higher than said reference level, said controller controls at least one of an effective value and a frequency of the driving voltage generated by said first inverter circuit such that the pressure detected by said first pressure detector approaches a first target value.

3. The gas generation device according to claim 1, further comprising:

a second pump having a motor and provided on said second gas discharge path;

a second inverter circuit that generates a driving voltage to be applied to the motor of said second pump; and

a second pressure detector that detects a pressure inside said second chamber, wherein

said controller controls at least one of an effective value and a frequency of the driving voltage generated by said second inverter circuit such that the pressure detected by said second pressure detector approaches a second target value.

4. The gas generation device according to claim 1, further comprising:

a first pressure detector that detects a pressure inside said first chamber;

a second pump having a motor and provided on said second gas discharge path;

in the case where the liquid level detected by said liquid level detector is not higher than said reference level, said controller controls at least one of an effective value and a frequency of the driving voltage generated by said first inverter circuit such that the pressure detected by said first pressure detector approaches a first target value, and also controls at least one of an effective value and a frequency of the driving voltage generated by said second inverter circuit such that the pressure detected by said second pressure detector approaches a second target value that is smaller than said first target value.

5. The gas generation device according to claim 1, further comprising:

a first open/close valve provided on said first gas discharge path; and

a second open/close valve provided on said second gas discharge path, wherein

said controller opens said first and second open/close valves in the case where electrolysis is carried out in said electrolyzer, and closes said first and second open/close valves in the case where no electrolysis is carried out in said electrolyzer.

6. The gas generation device according to claim 1, wherein said first chamber is a cathode chamber, and said second chamber is an anode chamber.

7. The gas generation device according to claim 1, wherein said second gas is fluorine.

8. A gas generation method for generating a first gas and a second gas by electrolysis by using an electrolyzer divided into a first chamber and a second chamber, the method comprising the steps of:

generating the first and second gases in said first and second chambers, respectively, by applying a voltage to an electrolytic bath contained in said electrolyzer, and discharging the first and second gases generated in said first and second chambers through first and second gas discharge paths, respectively;

controlling, by a first pump having a motor, the discharge of the first gas through said first gas discharge path;

detecting a liquid level of the electrolytic bath in said second chamber;

applying a driving voltage to the motor of said first pump by a first inverter circuit; and

in the case where said detected liquid level is higher than a predetermined reference level, controlling said first inverter circuit such that at least one of an effective value and a frequency of the driving voltage being applied to the motor of said first pump increases.

9. The gas generation method according to claim 8, further comprising the steps of:

detecting a pressure inside said first chamber;

in the case where said detected liquid level is not higher than the predetermined reference level, controlling at least one of an effective value and a frequency of the driving voltage generated by said first inverter circuit such that said detected pressure inside said first chamber approaches a first target value;

controlling, by a second pump having a motor, the discharge of the second gas through said second gas discharge path;

applying a driving voltage to the motor of said second pump by a second inverter circuit;

detecting a pressure inside said second chamber; and

controlling at least one of an effective value and a frequency of the driving voltage generated by said second inverter circuit such that said detected pressure inside said second chamber approaches a second target value that is smaller than said first target value.