JPS5826515B2 - How to start up and operate an air separation device - Google Patents

Description

Detailed Description of the Invention The present invention is a pretreatment device for an air separation device for producing oxygen (02) = nitrogen (N2), etc. from air, that is, carbon dioxide in the air supplied to a rectification column of the air separation device. Gas (CO2)
, and a method of operating an apparatus for removing impurities such as moisture (N20).

02. from the air. Air separation equipment that separates and recovers N2, etc. is operated at low temperatures, so CO□ and N2 present in the air are
0 will condense and solidify, interfering with the operation of the equipment.

Removal of impurities such as CO2 and N20 is conventionally performed by using a heat exchanger (reversible heat exchanger) between raw air and 02°N2, etc., separated in a rectification column of an air separation device.

Due to long-term operation, N20 was added to the heat exchanger. CO2
Impure N2 is introduced into this heat exchanger from a rectification column to prevent a large amount of N20. from precipitating and blocking the flow path.
It vaporizes CO2.

However, this requires a large amount of impure N2,
Normally, the amount of impure N2 occupies about 70% of the raw material air.

As a result, there is a problem in that the combined product recovery rate of pure 02 and pure N2 is only about 30% of the raw material air.

Therefore, the present inventors have already proposed a pretreatment device for an air separation device using a pressure difference adsorption method in order to improve the product recovery rate.

This pretreatment equipment is equipped with two adsorption towers filled with an adsorbent made of zeolite or the like, and raw air pressurized by a switching valve is introduced into one of the adsorption towers, and the N20 in the raw air is extracted under pressure. After CO2 is adsorbed and removed, it is fed to a heat exchanger and a rectification column.

On the other hand, impure N2 from the rectification tower is introduced into the adsorption tower that has already adsorbed N20°CO2, and the N20. CO2 is desorbed.

In this way, the adsorption operation and desorption operation are performed alternately using the switching valve.

In the pretreatment device for an air separation device using this pressure difference adsorption method, the yield of pure N2 obtained from the rectification column is greatly improved.

However, with this device, during trial operation, that is, when newly filled with adsorbent, when restarting after stopping the operation for periodic inspection, or when restarting when the adsorbent is contaminated due to a failure of the switching valve, etc. At the start of operation, it is necessary to regenerate the adsorbent in advance.

In such cases, nitrogen gas is flowed into the adsorption tower to regenerate the adsorbent.

However, it takes a relatively long time to regenerate the adsorbent, and the amount of nitrogen gas consumed is also large.

Furthermore, since the amount of pure 02 or pure N2 used, that is, the load, changes over time in the air separation device, it is also necessary to change the amount of raw air supplied to the air separation device.

For this purpose, a pressure regulating valve is operated so that the pressure in the piping supplying pressurized raw air to the adsorption tower does not exceed a set value, and excess pressurized air is released into the atmosphere.

Therefore, there is a problem in that the power for compressing the raw air is wasted.

An object of the present invention is to provide an operating method for efficiently regenerating an adsorbent that has adsorbed N20 and CO2 regarding a pretreatment device for an air separation device using a pressure difference adsorption method.

The present inventors investigated the relationship between the CO2 concentration in the feed air that has undergone adsorption treatment and the ratio of impure N2 to the amount of feed air (purge ratio) and obtained the results shown in FIG.

That is, in FIG. 1, as the purge ratio increases, the regeneration efficiency of the adsorbent in the desorption operation improves, and the CO2 concentration decreases.

Furthermore, the present inventors used adsorbed N20 instead of impure N2 in the desorption operation. It has been found that results similar to those shown in FIG. 1 can be obtained even when raw air from which CO2 has been removed is used.

The present invention has been made based on the above findings, and in the operation of an air separation pretreatment device using pressure difference adsorption method,
The raw air that has undergone adsorption treatment is used to regenerate the adsorbent.

That is, in the present invention, at the start of operation, that is, at the time of trial operation or restart, a pretreatment device using a pressure difference adsorption method is operated independently, and N20. By using the entire amount of air from which CO2 has been removed for the desorption operation, the adsorbent can be efficiently regenerated without using nitrogen gas for regeneration.

The present invention will be explained below based on the embodiment shown in FIG.

Raw air is pressurized to a predetermined pressure by a compressor 1, and cooled water 12
is cooled by the cooler 2 in which it is flowing, passes through the receiver tank 45, and then is sent to the adsorption tower 21 via the pipe 8 and the switching valve 23.

In this adsorption tower 21, N20. After performing an adsorption operation to remove CO2, the raw air is sent to the heat exchanger 32 via the switching valve 27, piping 57, and piping 41, where the pure N2. Pure 02. After cooling by heat exchange with impure N2, pipe 15 and pipe 19
It is supplied to the rectification column 7 via the expansion turbine 6 and the expansion turbine 6.

This raw material air is liquefied and rectified in a rectification column 7 using the difference in boiling point to separate 02 and N2. Pure N2 and impure N2 are produced.

Here, impure N2 is the remaining component in the air after removing pure 02 and pure N2, and usually has an N2 concentration of about 95%.

Pure N2 is recovered as a product via piping 9, heat exchanger 32, and piping 17.

Pure 02 is recovered as a product via piping 10, heat exchanger 32, and piping 18.

In addition, after the impure N2 passes through the pipe 11 and the heat exchanger 32,
After a desorption operation is performed to desorb the N20°CO2 that is supplied to the adsorption tower 22 via the pipes 42, 56, and the switching valve 30 and accumulated in the adsorbent made of zeolite or the like in the adsorption tower 22, the switch is performed. It is discharged to the outside of the system via the valve 26, piping 43, and piping 44.

Next, the adsorption tower system through which the raw air and impure N2 flow is switched at regular intervals, and the raw air is heat exchanged via piping 8, switching valve 25, adsorption tower 22, switching valve 29, piping 57, and piping 41. is supplied to the vessel 32.

On the other hand, the impure N2 that has passed through the heat exchanger 32 is transferred to the pipe 42 and the pipe 56.
, the switching valve 28, the adsorption tower 21, the switching valve 24, the piping 43, and the piping 44 to be discharged to the outside of the system.

In this way, adsorption operations and desorption operations are performed alternately in the adsorption towers 21 and 22 using the switching valves 23 to 30.

The above explanation is about how to operate the air separation equipment during normal operation, but it is important to note that during test runs, that is, when newly filling adsorbent, when restarting after stopping operation for periodic inspection, etc., when switching valve failure, etc. The adsorbent must be regenerated in advance at the start of operation, such as when restarting when the adsorbent becomes contaminated.

At the start of such operation, the pretreatment device is operated with valves 52 and 53 closed.

That is, the pressurized raw material air guided through the pipe 8 is subjected to adsorption treatment via the switching valve 23, the adsorption tower 21, and the switching valve 28.

The pressure of this adsorbed raw material air is lowered by the pressure regulating valve 51, and the air is used as a gas for desorption processing via the switching valve 30, the adsorption tower 22, and the switching valve 26.

Next, the system of the adsorption tower through which the raw air and adsorption-treated raw air flow is switched at regular intervals, and the raw air is transferred to the pipe 8,
Flowing through the switching valve 25, adsorption tower 22, and switching valve 29,
The adsorption-treated raw air flows through the pressure valve 51, the switching valve 28, the adsorption tower 21, and the switching valve 24.

In this way, using the switching valves 23 to 30, the adsorption tower 21
Adsorption operation and desorption operation are performed alternately in the adsorption tower 22.

These operations are performed until the adsorbents in the adsorption towers 21 and 22 are regenerated to a predetermined state.

After the adsorbent is regenerated to a predetermined state, the valves 52 and 54 are opened, and part of the raw air in the pipes 57 and 41 flows into the air separation device, and the system 4 is replaced.

Thereafter, valve 53 is opened and valve 54 is closed to start the air separation device.

Here, the purge ratio, that is, the ratio of the amount of gas flowing through the pipe 56 and the amount of gas flowing through the pipe 5γ, is controlled to be equal to or higher than the purge ratio during steady operation.

When replacing the air in the air separation device with gas, the air supplied to the air separation device is contaminated with CO2H20 present in the device, so it cannot be used for adsorbent regeneration and is blown away.

Therefore, for adsorbent regeneration, it is necessary to use air that has been subjected to adsorption treatment, and in order to maintain the adsorbent regeneration level, the purge ratio must be set to the value required for rated operation (0, 4
) or more.

This allows smooth operation from preliminary regeneration of the adsorbent to steady operation.

Next, during the steady operation described above, if the usage amount of pure 02 or pure N2 recovered from the air separation device fluctuates, and this causes a load fluctuation, the adsorption tower 21, the switching valve 27
The adsorption-treated raw material air flowing through the pipe 57 via the pressure regulating valve 51 flows into the adsorption tower 22 via the pipe 56 and the switching valve 30.

During this operation, impure N2 supplied from the comparator 32 via the pipe 42 is introduced into the adsorption tower 22 via the switching valve 30.

As described above, when the air separation device starts operating, the pretreatment device of the air separation device can be operated independently to efficiently desorb the adsorbent, so that the adsorbent is not supplied to the main body of the air separation device. The H2O and CO2 concentrations in the feed air can be reduced, and the air separation device can be operated efficiently and stably.

In addition, during steady operation of the air separation equipment, surplus feed air generated due to load fluctuations can be used for adsorbent desorption operations, so the power for compressing the feed air can be used effectively while maintaining the stability of the equipment. You can plan your driving.

Example: A pretreatment device using a pressure adsorption method (in Fig. 2, the device from the compressor 1 to the front stage of the heat exchanger 32) was used alone with a cycle time of 20 mm, an adsorption pressure of 5 kg/crit G, and a desorption pressure of 0.1 kg. /i-G, 5V-1 under the condition of purge ratio 1.0 (all raw air after adsorption operation is used in desorption operation)
000h-' and 5V=2000h-1.

FIG. 3 shows the change in CO2 concentration during the adsorption operation at a point where the filling height from the feed air inlet of the adsorption tower 21 is 70 widths of the total filling height.

According to Figure 3, the CO2 concentration decreases over time,
This shows that the regeneration of the adsorbent is progressing.

Looking at S■, the initial playback speed is S■2000h.
'A is thicker, but B with S■=1000h-1 has a lower CO2 concentration.

From these results, it is possible to regenerate the adsorbent by operating the pretreatment device alone, and it is also possible to perform the operation with the amount of feed air below the rated load of the air separation device, for example, by reducing the compressor load. It can be seen that it can also be operated at 1/2 of the rated load.

Here, H2O and CO in the raw air subjected to adsorption operation
Both concentrations were below lppm.

After 8 hours of operation at 5V=2000h-'', a portion of the raw air that had undergone the adsorption operation was sent to the air separation device, and the H2O and CO2 concentrations in the raw air were measured.

FIG. 4 shows the relationship between CO2 concentration and purge ratio.

The CO2 concentration was 1ppm or less when the purge ratio was 0.4 or more.

Therefore, in the above operation, it is desirable to use a large amount of air in the desorption operation, and if the CO2 concentration is desired to be pm or less, it is desirable to maintain the purge ratio at 0.4 or more.

This result shows that it is sufficient to set the purge ratio above the value during steady operation shown in FIG. 1.

Note that the H20 concentration was below ippm in all cases.

On the other hand, when the feed air load of the air separation device becomes 3/4 of the rated value, the excess air is discharged via the pressure regulating valve 46 in Fig. 2, and the desorption operation is performed via the pressure regulating valve 51. A comparison was made when used in

As a result, the CO2 concentration in the raw air after the adsorption operation is
It was found that the latter decreased to about 70 times the former.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the CO2 concentration and purge ratio in the adsorption-treated raw air, Fig. 2 is a flow diagram of the apparatus in which the present invention is implemented, and Fig. 3 is the carbon dioxide concentration in the adsorption tower in the example. FIG. 4 is a diagram showing the relationship between the raw material air amount ratio and the CO2 concentration during desorption and adsorption operations. DESCRIPTION OF SYMBOLS 1... Compressor, 2... Cooler, 6... Expansion turbine, 7... Rectification column, 21.22... Adsorption tower, 32...
...Heat exchanger, 45...Reverse tank.

Claims (1)

[Claims] 1. Introducing pressurized feed air into a pretreatment device including two or more adsorption towers connected in parallel to adsorb and remove carbon dioxide and moisture in the feed air in advance, and removing the carbon dioxide from one of the adsorption towers. introducing the adsorption-treated raw air into the other adsorption tower to desorb and regenerate the adsorbent in the other adsorption tower under a pressure lower than that of the one adsorption tower, and taking out the desorption gas from the system; A method for operating an air separation device, the method comprising introducing the adsorption-treated feed air into a heat exchanger and introducing it into a rectification column while cooling it to perform air separation, the method comprising: Regenerating the adsorption tower by cutting off the path to the exchanger and repeating pressure difference adsorption and desorption in the processing device, and after the adsorption tower has been regenerated to a predetermined state,
An air separation device characterized in that a part of the adsorption-treated raw air is flowed into the heat exchanger and the rectification column to be purified using the flow between the pretreatment device and the heat exchanger, and then activated. How to drive.