JP2741889B2 - Gas separation device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation device, and more particularly to a PSA (Pressure type) device.
The present invention relates to a gas separation device suitable for use as, for example, a nitrogen generator or an oxygen generator.

2. Description of the Related Art Generally, a PSA-type gas separation device separates air into nitrogen and oxygen using an adsorbent made of molecular sieve carbon,
One of them is taken out as product gas and used.

For this reason, for example, in a PSA type nitrogen generator (for example, see Japanese Utility Model Application No. Sho 62-172041), an adsorption step in which compressed air is introduced into an adsorption tower filled with an adsorbent to increase the pressure, and The desorption step of releasing the inside of the adsorption tower to the atmosphere or depressurizing with a vacuum pump is repeated.In the adsorption step, oxygen molecules are adsorbed by the adsorbent in the adsorption tower, and nitrogen is extracted to the outside. Is desorbed to prepare for the next adsorption step. (This series of steps is described below.
OK mode).

In addition, in order to efficiently generate high-purity product gas (for example, nitrogen gas) in a short time from the start of startup, and to recover the product gas concentration promptly during operation during the operation, an adsorption step (however, After the product gas is not discharged into the product tank, the product gas in the product tank is recirculated into the adsorption tower (hereinafter, this process is referred to as NG mode. See Japanese Utility Model Application No. 62-172041).

Further, the gas separator is provided with an air dryer for dehumidifying the compressed air from the compressor so that the concentration of the product gas does not change depending on the temperature (Japanese Utility Model Application No. 63-63).
66388). This air dryer cannot perform dehumidification at the same time as startup due to its structure, and requires a preparation exercise for about 5 minutes (hereinafter, this step is referred to as a preparation mode). Then, after the preparation mode ends, the compressor is started and the air dehumidified by the air dryer is introduced into the adsorption tower.

On the other hand, the gas separation device includes a sensor (generally using an O ₂ sensor) that measures the concentration of product gas introduced into the product tank near the product tank, a solenoid valve that constitutes the gas separation device including this sensor, and a compressor. A control means (sequencer) for controlling switching between the above modes and the like is provided.

In the conventional gas separation device having the above configuration (hereinafter simply referred to as a device), when a start switch is turned on, the sequencer puts the device in a preparation mode, performs a preparation movement of the air dryer,
Thereafter, the sequencer was configured to appropriately switch between the OK mode and the NG mode according to the concentration signal from the sensor and supply only the high-purity product gas to the product tank.

Problems to be Solved by the Invention However, the above-described conventional apparatus has only three modes: the preparation mode, the OK mode, and the NG mode, and thus has the following problems.

After the preparation mode ends, even if air is supplied to the adsorption or the like to perform the adsorption, a product gas having a purity equal to or lower than a predetermined purity comes out. This is because in the stopped state, the adsorbing state of the adsorbent contained in the adsorption tower is different from the state in which the adsorbent is repeatedly adsorbed and desorbed (the state in the OK mode), so that the predetermined capacity is not exhibited. In addition, the time required for obtaining the predetermined capability requires a long stopping time. For this reason, by setting the NG mode, the apparatus repeats the adsorption step and the reflux step, and eventually a product gas having a predetermined purity is generated. Then, the sensor detects this, and the sequencer which has received the signal from the sensor puts the device in the OK mode, and the product gas is immediately stored in the product tank.

However, the state in which the above-mentioned sensor detects the predetermined purity is a state in which the concentration of the product gas has finally reached the predetermined value, and in this state, the product gas is discharged toward the product tank and the pressure in the adsorption tower decreases. Then, the concentration of the product gas immediately becomes lower than the predetermined concentration again, and the apparatus may be in the NG mode. As described above, in the conventional apparatus, switching between the OK mode and the NG mode is frequently performed at the time of startup, and it takes a long time to operate in the NG mode, so that stable product gas cannot be generated and the product gas concentration decreases. There was a problem that it was easy to do.

In addition, a state similar to the above occurs even in an operation state after a while after the start. That is, it is assumed that the concentration of the product gas decreases during operation and the apparatus enters the NG mode, and thereafter, the usage amount of the product gas increases, the gas concentration exceeds a predetermined value, and the apparatus enters the OK mode. At this time, the pressure in the tower decreases, and the concentration of the product gas decreases accordingly, and the mode is switched again to the NG mode.
Therefore, even during operation, the OK mode and the NG mode are frequently switched (the number of occurrences is smaller than at the time of starting), and there is a problem that the product gas concentration may be reduced.

The present invention has been made in view of the above points, and an object of the present invention is to provide a gas separation device that can stably generate a high-purity product gas and that can shorten a so-called rise time particularly at the time of startup. .

Means for Solving the Problems In order to solve the above problems, in the present invention, a compressed raw material gas is supplied to an adsorption tower filled with an adsorbent, and a product gas generated by the adsorbent is taken out. In a gas separation device that accumulates pressure in a product tank, a concentration detection means for detecting the concentration of product gas to be generated is provided, and the adsorption step and the desorption step following this are defined as one cycle.
Step of supplying the above product gas to the product tank in the above adsorption process by operating the cycle as one unit (OK mode)
And the process of operating the adsorption process and the reflux process as one unit to increase the product gas concentration and pressure in the adsorption tower (NG mode)
And the same operation as in the OK mode except that the product gas is not supplied to the product tank (initial mode)
And a step (WA mode) of performing the same operation as the OK mode except that the product gas is not supplied to the product tank in the first one cycle operation based on the concentration detection signal from the concentration detecting means. Control means for performing the following.

Operation In the gas separation device configured as described above, the state of the device can be selected and set from four modes of an OK mode, an NG mode, an initial mode, and a WA mode based on the concentration of the product gas.

The OK mode is a mode that should be selected when the pressure in the adsorption tower and the product gas concentration are sufficiently increased because the product gas is supplied to the product tank from the beginning.

The NG mode is a mode in which the adsorption operation and the reflux operation are repeatedly performed, and thus should be selected when the pressure in the adsorption tower and the product gas concentration significantly decrease during operation.

The initial mode performs the same operation as the OK mode, but the generated product gas remains in the adsorption tower because it is not supplied to the product tank. Therefore, the pressure and product gas concentration in the adsorption tower rapidly increase, and this is a mode that should be selected particularly at the time of starting.

Further, in the WA mode, the supply of the product gas to the product tank is waited until one cycle is completed in the OK mode, and the pressure and the product gas concentration in the adsorption tower increase by one cycle. Therefore, the WA mode is a mode to be selected when switching from the initial mode to the OK mode and when switching from the NG mode to the OK mode.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a nitrogen generator (hereinafter simply referred to as an apparatus) as one embodiment of a gas separation apparatus according to the present invention. In this embodiment, an apparatus having two adsorption towers will be described.

In the figure, reference numerals 1 and 2 denote first and second adsorption towers, and each of the adsorption towers 1 and 2 is filled with molecular sieve carbon 1A and 2A, respectively.

Reference numeral 3 denotes a compressor serving as a compressed air supply source. Compressed air from the compressor 3 is alternately supplied to the adsorption towers 1 and 2 via a dryer 3a and pipes 6 and 7, respectively. Air supply valves 8 and 9 each composed of an electromagnetic valve are provided in the middle of 6 and 7, respectively.

Further, the pipe 4 arranged on the upstream side of the compressor 3
An intake pipe for supplying atmospheric air as a raw material gas, and is connected to the intake side of the compressor 3. An intake valve 5 composed of an electromagnetic valve is disposed in the pipe 4, and the intake valve 5 is opened during operation of the apparatus.

Reference numerals 10 and 11 denote pipes for discharging gas from the adsorption towers 1 and 2 at the time of desorption, which are connected to a common discharge pipe 12, and the discharge pipe 12 discharges desorbed exhaust gas. In the middle of the pipes 10, 11, there are provided gas discharge valves 13, 14, which are electromagnetic valves for alternately discharging the desorbed exhaust gas in the adsorption towers 1, 2 every half cycle.

15 and 16 are extraction valve pipes for extracting nitrogen from the adsorption towers 1 and 2, respectively, and 17 is an extraction pipe connected to each of the pipes 15 and 16;
In the middle of 16, take-out valves 18 and 19, each of which is a solenoid valve that opens alternately under control described later for only a half cycle, are provided. The outlet pipe 17 is connected to a reflux tank 20.

Reference numeral 21 denotes a pipe communicating between the adsorption towers 1 and 2, 22 denotes a pressure equalizing valve including an electromagnetic valve provided in the middle of the pipe 21, and a pressure equalizing valve 22 is a predetermined pressure when a half cycle by the adsorption towers 1 and 2 is completed. Open the valve for a short time to equalize the pressure between the adsorption towers 1 and 2.

Reference numeral 23 denotes an extraction pipe connected to the reflux tank 20, and an electromagnetic valve 24 and a check valve 25 are provided in the middle thereof. Reference numeral 26 denotes a concentration meter (concentration detection means) connected to the reflux tank 20. An oxygen sensor is used for the concentration meter 26, and the concentration meter 26 measures the oxygen concentration in the reflux tank 20.

The concentration meter 26 monitors the concentration of oxygen contained in the nitrogen gas in the reducing tank 20, and outputs a signal of a current value proportional to the concentration of oxygen. That is, when the nitrogen concentration of the gas in each of the adsorption towers 1 and 2 decreases, the oxygen concentration in the reduction tank 20 inevitably increases, so that the concentration meter 26 reduces the nitrogen concentration in the reduction tank 20 to a low concentration. Can be detected. The oxygen concentration measurement signal from the concentration meter 26 is input to a control circuit 27 described later.

The oxygen sensor used in the densitometer 26 is a magnetic oxygen sensor utilizing the paramagnetism of oxygen molecules. When oxygen enters the electrolyte through the permeable membrane, an oxidation-reduction reaction occurs at the electrodes and a current flows. Electromagnetic oxygen sensors that are used, zirconia oxygen sensors that provide electrodes on the inner and outer surfaces of the zirconia magnetism, and use that an electromotive force is generated by the oxygen concentration, and the like are used.

Further, the control circuit 27 is a control means constituted by, for example, a microcomputer or the like, selects each mode described below based on a signal output from the densitometer 26, and controls each valve, compressor, dryer, etc. according to the selected mode. The control is performed.

The reflux tank 20 is connected in series to a product tank 28 that stores nitrogen gas as product gas via a pipe 23 and a check valve 25 and the like. An extraction pipe 29 for supplying nitrogen gas, which is a product gas, to the downstream side is connected to the product tank 28,
An extraction valve 30 and the like are provided in the middle of the extraction pipe 29.

Apparatus 31 having the above configuration, preparation mode, OK mode,
There are five modes: initial mode, NG mode, and WA mode. Hereinafter, the operation of the device 31 in each mode will be described.

Preparation Mode The preparation mode is a mode that is also provided in the conventional gas separation device, and is a mode in which the preparation operation is performed until the dryer 3a starts up after the start. This preparation mode is about 5
Although the control is performed for about a minute, the control circuit 25 has a timer, and the timer controls the preparation mode.
That is, when the start switch is turned ON, the control circuit 25
31 is set to the preparation mode, and the preparation mode is terminated after about 5 minutes have elapsed (for details, refer to the aforementioned Japanese Utility Model Application No. 63-66388).

OK Mode The OK mode is a mode in which product gas is generated in each of the adsorption towers 1 and 2 and accumulated in the product tank. The specific operation in the OK mode will be described with reference to FIG. 2 (note that a valve that is opened is shown in white and a valve that is closed is shown in black). FIG. 2 (A) shows a state in which the first adsorption tower 1 is in the desorption step and the second adsorption tower 2 is in the pressure increasing step. When the pressure of the second adsorption tower 2 is raised to a predetermined pressure, the extraction valve 19 is opened, and the product gas generated as shown in FIG. 2 (B) flows into the reflux tank 20. In the OK mode, the solenoid valve 24 is open, so that the product gas is supplied from the recirculation tank 20 to the product tank 28 via the solenoid valve 24 and the check valve 25, and stored therein. When the adsorption step in the second adsorption tower 2 is completed, the discharge valve 13 and the discharge valve 19 are closed and the pressure equalizing valve 22 is opened as shown in FIG. Move to pressure step.

Subsequently, as shown in FIGS. 2 (D) and 2 (E), the first adsorption tower 1 will become an adsorption step in the future to generate product gas,
Is a desorption step, and one cycle is completed in the pressure equalization step shown in FIG. 2 (F). The OK mode operates with the cycle shown in FIGS. 2A to 2F as one cycle and two cycles as one unit.

In the OK mode, the generated product gas is sequentially supplied to the product tank 28, and thus has a characteristic that the internal pressure of the adsorption tower and the product gas concentration in the adsorption step are reduced at the fastest rate as compared with other modes. I have.

Initial Mode The operation of the initial mode is substantially the same as the above-described OK mode, except that the solenoid valve 24 is closed during the operation of the mode. The operation in the initial mode is shown in FIGS.
This initial mode operates in units of one cycle shown in FIGS. 3A to 3F. As described above, in this mode, since the solenoid valve 24 is closed, the product gas flows into the recirculation tank. Stored in 20. Thus, in the initial mode, the internal pressure of the reflux tank 20 can be increased.

NG mode The NG mode includes a step of refluxing the gas stored in the reflux tank 20 during the process to each of the adsorption towers 1 and 2, and the purity of the product gas generated in the adsorption towers 1 and 2 in the adsorption step. This is performed for the purpose of improving and shortening the boosting time. The specific steps are shown in FIGS. 4 (A) to (D). still,
Also in this NG mode, the electromagnetic valve 24 is closed, and the product gas generated in each of the adsorption towers 1 and 2 is supplied to the product tank 28 and stored in the recirculation tank 20.

FIG. 4 (A) shows a state where the first adsorption tower 1 is in a desorption step and the second adsorption tower 2 is in a pressure increasing step. At this time, the compressor 3
Compressed air is introduced from above, and the product gas stored in the recirculation tank 20 flows by opening the take-out valve 19. Therefore, the pressure in the adsorption tower 2 is increased to a predetermined pressure in a short time, and the nitrogen concentration in the adsorption tower 2 has a higher value than when air is simply introduced. Eventually, the pressure of the compressed air becomes greater than the pressure of the recirculated product gas, and the adsorption tower 2 performs an adsorption step. FIG. 4 (B) shows a state where the adsorption tower 2 is in the adsorption step. At this time, the purity of the product gas stored in the recirculation tank 20 is a gas with higher precision than that obtained by simply adsorbing air for the above-described reason.

Subsequently, as shown in FIGS. 4 (c) and 4 (d), the same treatment is performed on the first adsorption tower 1, and a high-purity product gas is also supplied from the first adsorption tower 1 for reflux. The pressure is stored in the tank 20.

As described above, in the NG mode, the product gas concentration in the reflux tank 20 can be increased in a short time, and by repeating this mode, the concentration (purity) gradually increases. ing.

WA mode The WA mode is an intermediate mode between the OK mode and the initial mode. The WA mode also operates in two cycles as a unit, similar to the OK mode, but performs the same operation as the initial mode (ie, the solenoid valve 24 is closed) in the first one cycle, and then performs the second cycle Is configured to perform the same operation as the OK mode (that is, the electromagnetic valve 24 is opened).

In the WA mode, the supply of product gas to the product tank 28 is delayed by one cycle compared to the OK mode.
In order to perform an intermediate operation stored in the storage unit 20, it has a characteristic that a smooth switching can be performed by selecting the mode when switching each mode.

Each mode described above corresponds to the ROM in the control circuit 27.
When the CPU in the control circuit 27 selects a mode based on the density signal from the densitometer 26,
The device 31 is configured to perform each mode operation in accordance with each mode program stored in the ROM (see FIG. 1).

Next, control processing (mode selection processing) performed by the control circuit 27 will be described. FIG. 5 is a flowchart showing the processing performed by the control circuit 27.

When the start switch is turned on (Step 1, hereinafter, the steps are abbreviated as S), the control circuit 27 puts the device 31 into the preparation mode (S2). The preparation mode is time-managed as described above, and when a predetermined time has elapsed by the timer in the control circuit 27, the preparation mode ends.

When the preparation mode is completed, the control circuit 27 reads the concentration (Pn, where Pn is converted to nitrogen concentration) from the concentration meter 26, and determines whether or not this is higher than a predetermined product gas concentration (Po). Here, the concentration of the product gas in the reflux tank 20
If Pn is lower than the predetermined concentration Po, the control circuit 27
Is set to the initial mode (S4). Thus, the apparatus 31 performs the above-described initial mode operation, and product gas for one cycle is accumulated in the recirculation tank 20.

When the initial mode is completed, the control circuit 27 returns to the concentration meter 26 again.
Then, it is determined whether or not the concentration Pn of the product gas in the reflux tank 20 has reached the predetermined value Po (S5).
The determination of the product gas concentration (S3, S5) after the end of the preparation mode and after the end of the initial mode is performed when the device 31 is temporarily stopped after a long operation and is immediately started up. This is because, at the end of the mode, the product gas having the predetermined concentration Po may be generated immediately. Since the product gas concentration immediately becomes the predetermined concentration Po immediately after the completion of the preparation mode, the operation of the initial mode may be performed immediately after the completion of the preparation mode except for S3.

If it is determined in S5 that the predetermined concentration has not been reached,
The control circuit 27 sets the device 31 to the NG mode (S6). This NG mode is continued until the product gas in the recirculation tank 20 becomes equal to or higher than the predetermined concentration Po (S7).

On the other hand, when it is determined in S3, S5, S7 that the product gas concentration Pn in the recirculation tank 20 is higher than the predetermined concentration Po, the control circuit
27 sets the device 31 in the WA mode (S8), and after the WA mode ends, sets the OK mode (S9). This OK mode is continued until the concentration Pn of the product gas in the reflux tank 20 becomes equal to or lower than the predetermined concentration Po (S10), and the product gas generated in each of the adsorption towers 1 and 2 is supplied to the product tank. As described above, the product gas supplied to the product tank 28 is guaranteed to be equal to or higher than the predetermined concentration Po, and the reliability of the product gas can be improved.

Further, as is clear from the above description, in the device 31, the OK mode for supplying the product gas to the product tank 28 is changed from the preparation mode or the initial mode to the OK mode when the product gas concentration Pn is equal to or higher than the predetermined concentration Po. In this configuration, the mode switching is performed. As described above, since the most appropriate mode selection corresponding to the product gas concentration Pn is performed, the rise time required for product gas generation can be shortened, and product gas can be generated efficiently. In particular, at the time of startup, since the concentration determination (S3, S5) is performed after the preparation mode ends and the initial mode ends, the startup efficiency at the time of startup can be improved.

Further, even if the product gas concentration Pn is determined to be equal to or higher than the predetermined concentration Po after the preparation mode, the initial mode, and the NG mode (S3, S5, S7), the device 31 does not immediately enter the WA mode but enters the WA mode. After this, the mode is switched to the OK mode. Therefore, after the preparation mode and the initial mode performed at the time of the startup, even if the product gas concentration Pn becomes equal to or higher than the predetermined concentration Po, one cycle of the product gas is further accumulated in the recirculation tank 20 in the WA mode. Therefore, after the WA mode, the operation mode becomes the OK mode, the solenoid valve 24 is opened, and the product gas is supplied to the product tank 28.
Even if the pressure in product 1, 2 or the product gas concentration decreases, the product gas for one cycle is stored in the recirculation tank 20 in excess in the WA mode as compared with when the concentration reaches the predetermined concentration Po. The product gas concentration Pn in the adsorption towers 1 and 2 does not become lower than the predetermined concentration, and the apparatus 31 does not immediately return to the NG mode by S10.

Therefore, the product gas can be stably supplied to the product tank 28, and the purity of the product gas, which tends to occur at the time of mode switching, can be prevented from lowering. In addition, NG
Since the WA mode is performed even after the mode ends, the stable supply of the product gas and the decrease in the purity of the product gas can be prevented during the operation for the same reason as described above. S1
If it is determined in 1 that the stop switch has been turned on, the device 31
Stops (S11).

In this embodiment, an apparatus using two adsorption towers has been described as an example. However, it is needless to say that an apparatus using one or a plurality of adsorption towers can be applied.

Further, in the present embodiment, the gas separation device 31 having the configuration in which the recirculation tank 20 is provided separately from the product tank 28 has been described. However, the recirculation tank 20 is not always necessary, and as shown in FIG. The concentration meter 26 may be provided in the tank 32 so that the product tank 32 has a function as a reflux tank. According to the gas separation device 33 shown in FIG. 6, the structure can be simplified, the number of parts can be reduced, and the size of the device can be reduced as compared with the gas separation device 31 shown in FIG. In the gas separator 33, since there is no recirculation tank, the fluctuation of the product gas concentration in the product tank 32 becomes larger than that in the gas separator 1. However, the timing of opening the solenoid valve 30 must be appropriately performed. As a result, a product gas having a predetermined concentration can be supplied to the pipe 29, and there is no problem.

Effect of the Invention As described above, according to the present invention, the control unit can select the initial mode, the OK mode, the NG mode, and the WA mode based on the signal from the concentration detection unit, and thus the mode most suitable for the state in the adsorption tower. By selecting, the start-up time at the time of starting can be shortened, and the product gas can be stably generated at the time of starting and during operation, and the purity of the product gas can be maintained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the overall configuration of a gas separation device according to one embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the device in an OK mode, and FIG. 3 is a diagram showing the operation of the device in an initial mode. FIG. 4 is a diagram for explaining the operation of the apparatus in the NG mode, FIG. 5 is a diagram for explaining a process performed by the control circuit, and FIG. 6 is a modification of the present invention. It is a whole block diagram of a gas separation device. 1 1st adsorption tower, 2 2nd adsorption tower, 1A, 2A ...
Molecular sieve carbon, 3 ... Compressor, 3a ... Dryer, 20 ... Reflux tank, 24 ... Solenoid valve, 26 ... Densitometer, 27 ... Control circuit, 28 ... Product tank, 31 ... Equipment ( Gas separation device).

Claims (1)

(57) [Claims] 1. A gas separation apparatus for supplying a compressed raw material gas to an adsorption tower filled with an adsorbent, taking out a product gas generated by the adsorbent, and accumulating the product gas in a product tank. A step of providing a concentration detecting means for detecting the concentration of product gas, and a step of supplying the product gas to the product tank in the above-mentioned adsorption step by operating the adsorption step and the desorption step as one cycle, and two cycles as one unit ( OK mode), the process of operating the adsorption process and the reflux process as one unit to increase the product gas concentration and pressure in the adsorption tower (NG mode), and the above-mentioned OK except that the product gas is not supplied to the product tank Step that performs the same operation as the mode (initial mode) and the same operation as the OK mode except that the product gas is not supplied to the product tank in the first one cycle operation A gas separating apparatus comprising a control means for performing a switching operation based on a concentration detection signal from the concentration detection means.