TWI626214B - Purification method and purification system for carbonic acid gas - Google Patents

Abstract

The present invention provides a purification method and a purification system for carbon dioxide which can improve the purity of carbon dioxide purified by a pressure swing adsorption method without lowering the recovery rate.

In each of the adsorption towers 2a, 2b, and 2c, the adsorption step, the depressurization step, the desorption step, and the pressure increasing step are sequentially performed to adsorb the carbon dioxide contained in the raw material carbon dioxide to the adsorbent under pressure, and will not be The impurity gas adsorbed by the adsorbent is discharged as a gas. Performing a gas extrusion step of introducing the internal gas of any one of the adsorption towers in the depressurization step into any one of the adsorption towers in a state after the desorption step and before the pressure increasing step, The carbon dioxide remaining inside the adsorption tower which is in the state after the desorption step and before the pressure increasing step is pushed out to the outside. The carbon dioxide discharged from each adsorption tower in the desorption step and the carbon dioxide extruded in the gas extrusion step are recovered as a purified gas.

Description

Carbon dioxide purification method and purification system

The present invention relates to a method and system for obtaining high purity carbon dioxide at a high recovery rate by purifying a raw material carbon dioxide containing an impurity gas.

Carbon dioxide is used in a wide range of applications, such as for cryopreservation or cryogenic transportation of foods, foaming of beverages, welding, or as a fire extinguishing agent. Industrially, a gas system containing carbon dioxide discharged from petroleum purification equipment, ammonia production equipment, iron making equipment, beer manufacturing equipment, and the like is used as a raw material of carbon dioxide. The carbon dioxide of such a raw material is purified by containing an impurity gas such as hydrogen, methane, nitrogen, oxygen, carbon monoxide or the like to obtain high-purity carbon dioxide.

As a method for purifying a raw material carbon dioxide, a low-temperature separation method in which carbon dioxide is compressed and cooled to be separated from an impurity gas, and an amine absorption which is selectively separated from an impurity gas by an amine absorption liquid is known. The method uses a separation membrane to separate carbon dioxide from an impurity gas, and a pressure swing adsorption method (PSA, Pressure Swing Adsorption). Among these purification methods, a pressure swing adsorption method is used in consideration of the supply flow rate, cost, operation, and the like of the raw material carbon dioxide.

As a prior art for purifying a raw material carbon dioxide by a pressure swing adsorption method, a method using a pressure swing type adsorption device having a plurality of adsorption columns is known. In the pure In the method, the adsorbent which preferentially adsorbs carbon dioxide with respect to the impurity gas is accommodated in each adsorption tower. In each of the adsorption towers, a step of adsorbing carbon dioxide contained in the introduced raw material carbon dioxide to the adsorbent under pressure and discharging the impurity gas not adsorbed by the adsorbent; and desorbing The step of desorbing carbon dioxide from the adsorbent when the pressure is reduced (refer to Patent Document 1). The carbon dioxide subjected to the desorption step is recovered as a purified gas.

The desorption step is carried out by performing an adsorption step under pressure of atmospheric pressure to several tens of kPa (gauge pressure) inside the adsorption tower, and connecting the inside of the adsorption tower to a normal pressure space, and performing the desorption step after the vacuum treatment Compared with the case of the desorption step, a vacuum pump is not required, so that power cost and maintenance cost can be reduced.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4839114

In the prior art described in the above patent documents, there is a problem that the recovery rate is lowered and the cost advantage is small if the purity of the purified carbon dioxide is increased. Further, there is a problem that the quality of the purified carbon dioxide is unstable. It is an object of the present invention to provide a purification method and purification system for carbon dioxide which can solve the prior art problems of the pressure swing adsorption method.

In the method of the present invention, when the carbon dioxide containing the impurity gas is purified by using a pressure swing adsorption device having a plurality of adsorption columns, the adsorbent which preferentially adsorbs carbon dioxide with respect to the impurity gas is stored in each of the adsorption towers, The raw material carbon dioxide is sequentially introduced into each adsorption tower, and in each of the adsorption towers, the following steps are sequentially performed, and the carbon dioxide discharged from the adsorption towers in the desorption step is added as a purification gas. a method for purifying carbon dioxide recovered: an adsorption step of adsorbing carbon dioxide contained in the carbon dioxide of the raw material introduced into the adsorbent under pressure, and discharging the impurity gas not adsorbed by the adsorbent as an outgas a depressurization step for reducing internal pressure; a desorption step for desorbing and discharging carbon dioxide from the adsorbent; and a step of increasing the internal pressure; the method is characterized by: performing the following gas extrusion step The gas extrusion step is introduced into the other of the adsorption towers in the depressurization step by any one of the adsorption towers in a state after the desorption step and before the pressure increasing step. a gas which is desorbed to the outside of the inside of the adsorption tower which is in a state after the desorption step and before the step of the step of raising the pressure; the carbon dioxide which is extruded in the gas extrusion step is purified The gas is recovered.

The present invention is based on the following findings.

When the raw material carbon dioxide is purified by the pressure swing adsorption method to obtain high-purity carbon dioxide, the high-purity carbon dioxide desorbed from the adsorbent is retained inside the adsorption tower after the desorption step.

In the prior art, the high-purity carbon dioxide retained in the inside of the adsorption tower is partially adsorbed to the adsorbent in the subsequent adsorption step, but the remainder is discharged as an outgas from the adsorption tower, so that the recovery rate of carbon dioxide is lowered.

In this case, according to the present invention, a gas pressing step is performed by introducing into the depressurizing step by any one of the adsorption columns in a state after the desorption step and before the pressure increasing step. The internal gas of any of the other columns is adsorbed, and the retained carbon dioxide is pushed out to the outside; and the extracted carbon dioxide is recovered as a purified gas. That is, it is possible to avoid waste and recover high-purity carbon dioxide remaining inside the adsorption tower, thereby increasing the recovery rate of carbon dioxide.

The system of the present invention is provided with a pressure swing type adsorption device for purifying carbon dioxide containing a raw material containing an impurity gas, and the pressure swing type adsorption device has a gas relative to the impurity gas And a plurality of adsorption towers which preferentially adsorb the adsorbent of carbon dioxide, and have: an introduction flow path for introducing the carbon dioxide of the raw material into the adsorption towers; and an escape flow path for degassing from the respective adsorptions Discharged in the column; a purified gas flow path for discharging carbon dioxide from the respective adsorption towers; and a communication flow path for interconnecting any one of the adsorption towers with any one of the other; a valve for individually opening and closing between each of the adsorption towers and the introduction flow path; and an escape valve switching valve for individually opening and closing between the adsorption towers and the escape flow path; a switch valve for individually opening and closing between the adsorption towers and the purified gas flow path; and a communication path switching valve for individually opening and closing between the adsorption towers and the communication flow path Each of the above-described switching valves is an automatic valve having a switching actuator that can be individually switched and connected to the control device, and is sequentially implemented in each of the adsorption towers In the next step, the above-mentioned respective switching valves are controlled by the above-mentioned control device: an adsorption step of adsorbing carbon dioxide contained in the introduced raw material carbon dioxide to the adsorbent under pressure, and will not be adsorbed by the adsorbent The adsorbed impurity gas is discharged as an outgas; the depressurization step is to reduce the internal pressure; the desorption step is to desorb and discharge the carbon dioxide from the adsorbent; and the step of increasing the internal pressure; the characteristics of the system The control valve is configured to control the respective on-off valves by performing the gas pressing step, wherein the gas pressing step is performed by any one of the adsorption towers in a state after the desorption step and before the step of boosting The internal gas of any one of the adsorption towers in the depressurization step is introduced, and is retained in the inside of the adsorption tower in a state after the desorption step and before the pressure increasing step. The carbon dioxide is pushed out to the outside.

The method of the invention can be carried out in accordance with the system of the invention.

In the method of the present invention, in the gas extrusion step, it is preferable to change the adsorption tower from the adsorption tower to any one of the adsorption towers according to a change in the carbon dioxide concentration in the raw material carbon dioxide. The amount of gas introduced by one.

The internal gas of the adsorption tower in the depressurization step contains not only the impurity gas but also the carbon dioxide which is not adsorbed by the adsorbent, and the carbon dioxide concentration of the internal gas changes depending on the concentration of the carbon dioxide in the raw material carbon dioxide. Therefore, if the concentration of carbon dioxide in the raw material carbon dioxide is increased, the amount of gas introduced from any one of the adsorption towers in the gas extrusion step is increased, and if the concentration of carbon dioxide in the raw material carbon dioxide is decreased, the amount is decreased. The amount of the introduced gas can suppress the change in the purity of the carbon dioxide extruded in the gas extrusion step, and maintain the purity and recovery of the recovered carbon dioxide at a high level.

In this case, the system of the present invention preferably includes a flow rate control valve that regulates the flow rate of the gas flowing through the communication passage, and the flow rate control valve has a flow rate adjustment actuator as a flow rate adjustment operation. And an automatic valve connected to the control device, and having a sensor for detecting a carbon dioxide concentration of the raw material carbon dioxide and connected to the control device, wherein a predetermined execution time of the gas pressing step is stored in the control device In the gas extrusion step, the flow rate of the gas flowing through the communication passage when the internal gas of the adsorption tower in the depressurization step is introduced into any one of the adsorption towers, and the raw material The predetermined correspondence relationship between the carbon dioxide concentrations in the carbon dioxide is stored in the control device, and is changed to the adsorption tower in the gas extrusion step according to the change in the carbon dioxide concentration measured by the sensor. Any one of the above adsorption towers in the above-described depressurization step The embodiment of the gas amount, the above-described embodiment in order to control time of said memory means of an embodiment of the gas pressure step, and controlling the switching valve, and the changes the flow control regulator of the gas flow valve based on the correspondence relationship.

Alternatively, the system of the present invention preferably has a sensor for detecting the carbon dioxide concentration of the carbon dioxide of the raw material and connected to the control device, and a predetermined time between the execution time of the gas pressing step and the carbon dioxide concentration in the raw material carbon dioxide. Correspondence is stored in the above control device to determine the oxidization according to the sensor The change in the carbon concentration is changed to the amount of gas introduced from any one of the adsorption towers in the gas extrusion step, and the gas extraction is performed by the control device based on the correspondence relationship. The implementation time of the steps.

In the method of the present invention, it is preferred that the inside of the adsorption tower in a state after the gas extrusion step and before the pressure increasing step is after the pressure reduction step and before the desorption step In the other state, the inside of the adsorption tower is connected to the inside of the adsorption tower, and the pressure is increased in the adsorption tower after the gas extrusion step and the pressure increase step. The pressure equalization step is performed in any one of the adsorption towers after the pressure reduction step and before the desorption step.

Thereby, the adsorption tower in the pressure equalization step is pressurized by feeding the internal gas of the adsorption tower in the depressurization pressure equalization step, and the carbon dioxide contained in the supplied gas is followed by the adsorption step. It is adsorbed to the adsorbent. Therefore, the recovery rate of carbon dioxide can be improved.

In the method of the present invention, it is preferred to use a compressed gas as the raw material carbon dioxide, and pressurize the inside of the adsorption tower to the adsorption pressure required in the adsorption step by the pressure of the raw material carbon dioxide, thereby making the inside of the adsorption tower Connect to the atmospheric space and depressurize to the pressure required in the desorption step described above.

Therefore, it is not necessary to provide a dedicated device for pressurizing or depressurizing the inside of the adsorption tower, and it is possible to reduce power cost, maintenance cost, and the like, and since vacuum operation is not performed, air is not mixed from the outside, and thus it is related to Maintenance of quality.

According to the present invention, the purity of carbon dioxide purified by the pressure swing adsorption method can be improved without lowering the recovery rate, and carbon dioxide of stable quality can be obtained.

1‧‧‧Variable pressure adsorption device

2a, 2b, 2c‧‧‧ adsorption tower

2a', 2b', 2c', 2a", 2b", 2c"‧‧‧ gas passage

3‧‧‧Introduction piping (introduction flow path)

4‧‧‧Yi gas piping (Yi air flow)

5‧‧‧Purified gas piping (purified gas flow path)

6a, 6b, 6c‧‧‧1st to 3rd on-off valves (introduction switch valves)

7a, 7b, 7c‧‧‧4th to 6th on-off valves (airway switch valves)

8a, 8b, 8c‧‧‧7th to 9th on-off valves (purified gas circuit switching valves)

9‧‧‧Connected piping (connected flow path)

9a, 9b, 9c‧‧‧1st to 3rd communication

10a, 10b, 10c, 11a, 11b, 11c, 12, 14‧ ‧ 10th to 17th on-off valves (communication switch valves)

13‧‧‧1st flow control valve

15‧‧‧2nd flow control valve

20‧‧‧Control device

21‧‧‧Flow Sensor

22‧‧‧Buffer box

23‧‧‧ Pressure Sensor

24‧‧‧ concentration sensor

25‧‧‧3rd flow control valve

26a‧‧‧1st pressure regulating valve

26b‧‧‧2nd pressure regulating valve

27a, 27b, 27c‧‧‧ pressure sensors

28‧‧‧ Input device

29‧‧‧ Output device

100‧‧‧Variable pressure adsorption device

G1‧‧‧ raw material carbon dioxide

G2‧‧‧ 逸气

G3‧‧‧purified gas

G3'‧‧‧purified gas

G4‧‧‧ internal gas

G5‧‧‧ internal gas

α‧‧‧CO2 purification system

Fig. 1 is an explanatory view showing the configuration of a pressure swing type adsorption apparatus according to an embodiment of the present invention.

Fig. 2 is an explanatory view showing a control device of a purification system according to an embodiment of the present invention.

Fig. 3 is a view showing operational states (a) to (i) of the pressure swing adsorption apparatus according to the embodiment of the present invention.

Fig. 4 is a view showing the operational state of the pressure swing adsorption apparatus according to the embodiment of the present invention, the purification processing procedure in each adsorption tower, and the correspondence relationship with the state of the on-off valve.

Fig. 5 is an explanatory view showing the configuration of another pressure swing type adsorption device.

Fig. 6 is a view showing an operational state (a) '~(f)' of the pressure swing adsorption apparatus of the comparative example.

Fig. 7 is a view showing the operational state of the pressure swing adsorption apparatus of the comparative example, the correspondence between the purification processing steps in each adsorption tower, and the state of the on-off valve.

The carbon dioxide purification system α according to the embodiment of the present invention shown in Fig. 1 includes a pressure swing adsorption device 1 for purifying a raw material carbon dioxide G1 containing an impurity gas.

The pressure swing adsorption apparatus 1 has a plurality of adsorption towers 2a, 2b, and 2c, and accommodates adsorbents that preferentially adsorb carbon dioxide with respect to the impurity gas in each of the adsorption towers 2a, 2b, and 2c. In the present embodiment, the first to third adsorption towers 2a, 2b, and 2c are provided, and gas passage openings 2a', 2b', 2c', and 2a are formed at one end and the other end of each of the adsorption towers 2a, 2b, and 2c. ", 2b", 2c".

The adsorbent contained in each of the adsorption towers 2a, 2b, and 2c is not particularly limited as long as it can preferentially adsorb carbon dioxide with respect to the impurity gas, and a carbon molecular sieve or zeolite can be used. In particular, when carbon dioxide is adsorbed under pressure and desorbed in the vicinity of normal pressure, it is preferred to fill the adsorption columns 2a, 2b, and 2c with carbon molecular sieves as adsorbents. In the case of using a carbon molecular sieve, it is preferred that the average pore diameter is 1.5 to 2.0 nm and the specific surface area is 1000 m ² /g or more. Further, it is preferably an adsorption capacity separation type.

The introduction pipe 3, the escape pipe 4, and the purified gas pipe 5 are connected to each of the adsorption towers 2a, 2b, and 2c.

One end of the introduction pipe 3 is connected to a supply source of the raw material carbon dioxide G1. Import piping The other end of the third branch is branched into three to the first to third adsorption towers 2a, 2b, and 2c, and is connected to the adsorption tower via the first to third on-off valves 6a, 6b, and 6c that constitute the inlet-side switching valve. The gas at one end of each of 2a, 2b, and 2c passes through the ports 2a', 2b', and 2c'. Thereby, the introduction pipe 3 constitutes an introduction flow path for introducing the raw material carbon dioxide G1 into each of the adsorption towers 2a, 2b, and 2c. In addition, by using the first to third on-off valves 6a, 6b, and 6c, the adsorption towers 2a, 2b, and 2c are individually opened and closed between the introduction channels 2a, 2b, and 2c, and the raw material carbon dioxide G1 can be introduced into the flow path. Individually introduced into each of the adsorption towers 2a, 2b, and 2c.

The raw material carbon dioxide G1 is supplied, for example, from a supply source such as a petroleum purification equipment, an ammonia production facility, a steelmaking facility, or a beer manufacturing facility, and is a mixed gas of an impurity gas such as hydrogen, methane, nitrogen, oxygen, carbon monoxide, or the like. The raw material carbon dioxide G1 supplied from the supply source of the present embodiment is a compressed gas having a pressure of about 2 MPa (gauge pressure). In addition, when the raw material carbon dioxide G1 supplied from the supply source is not a compressed gas, it may be compressed by a compressor or the like.

One end of the escape pipe 4 is branched into three in the first to third adsorption towers 2a, 2b, and 2c, and is connected via the fourth to sixth on-off valves 7a, 7b, and 7c that constitute the escape valve. The gas at the other end of each of the adsorption towers 2a, 2b, and 2c passes through the ports 2a", 2b", and 2c". The other end of the escape pipe 4 serves as an outlet of the outgas G2 to the atmospheric pressure space under atmospheric pressure. Therefore, the escape pipe 4 constitutes an escape flow path for discharging the escape gas G2 from the adsorption towers 2a, 2b, 2c to the normal pressure space. Further, by using the fourth to sixth on-off valves 7a, 7b And 7c, the respective adsorption towers 2a, 2b, 2c and the escape flow path are individually opened and closed, and the outgas G2 can be individually discharged from each of the adsorption towers 2a, 2b, 2c. The discharged escape gas G2 is discharged to the outside of the adsorption device 1.

The first pressure regulating valve 26a for back pressure adjustment can be provided in the escape pipe 4, and the internal pressure in each of the adsorption towers 2a, 2b, and 2c can be adjusted to a predetermined adsorption pressure in the adsorption step. The adsorption pressure may be a value suitable for adsorption below the pressure of the raw material carbon dioxide G1 and exceeding atmospheric pressure.

One end of the purified gas pipe 5 is branched into three to the first to third adsorption columns 2a, 2b, and 2c, and is connected via the seventh to ninth on-off valves 8a, 8b, and 8c constituting the purified gas passage switch valve. The gas passing through one of the adsorption towers 2a, 2b, 2c passes through the ports 2a', 2b', 2c'. The other end of the purified gas pipe 5 serves as an outlet for the purified gases G3 and G3' and leads to a normal pressure space. Further, the second pressure regulating valve 26b for adjusting the back pressure can be provided in the purification gas pipe 5 to adjust the adsorption gas G3, G3' in the desorption step so as to have a predetermined pressure. Internal pressure. Thereby, the purified gas pipe 5 constitutes a purified gas flow path for discharging the purified gases G3 and G3' from each of the adsorption columns 2a, 2b, and 2c. Further, by using the seventh to ninth on-off valves 8a, 8b, and 8c, the respective adsorption towers 2a, 2b, and 2c are individually opened and closed between the purification gas flow paths, and the purified gases G3 and G3' can be self-contained. Each of the adsorption towers 2a, 2b, and 2c is individually discharged and recovered. The recovered purified gases G3 and G3' can be stored, for example, in a specific container, or can be directly supplied from a purified gas flow path in a subsequent step such as a liquefaction apparatus, and the use is not limited.

A communication pipe 9 is provided, and the communication pipe 9 constitutes a communication flow path for connecting any one of the adsorption towers 2a, 2b, and 2c to each other. The communication pipe 9 has a first communication portion 9a, a second communication portion 9b, and a third communication portion 9c. One end of the first communication portion 9a is branched into three in the first to third adsorption towers 2a, 2b, and 2c, and is connected via the tenth to twelfth switching valves 10a, 10b, and 10c that constitute the communication path switching valve. The gas passing through the ports 2a", 2b", and 2c" at the other end of each of the adsorption towers 2a, 2b, and 2c. The one end of the second communication portion 9b is oriented toward the first to third adsorption towers 2a, 2b, and 2c. Three branches are branched, and the gas passage ports 2a", 2b", and 2c are connected to the other ends of the adsorption towers 2a, 2b, and 2c via the 13th to 15th on-off valves 11a, 11b, and 11c constituting the communication path switching valve. ". The other end of the first communication portion 9a and the other end of the second communication portion 9b pass through the 16th on-off valve 12 constituting the communication passage opening and closing valve and the first flow control valve constituting the flow rate of the gas flowing through the communication passage. The flow control valves 13 are connected to each other. One end of the third communication portion 9c is configured to flow through the 17th on-off valve 14 constituting the communication path switching valve and the flow rate of the gas constituting the flow in the communication passage. The second flow rate control valve 15 of the control valve is connected to the first communication portion 9a and the second communication portion 9b. The other end of the third communication portion 9c is connected to the escape pipe 4. Thus, by individually opening and closing each of the adsorption towers 2a, 2b, 2c and the communication flow path, any one of the adsorption towers 2a, 2b, 2c can be switched to each other. A state in which they are opened and connected to each other, and are in a state of being closed and not connected to each other.

Each of the first to seventeenth on-off valves 6a, 6b, 6c, 7a, 7b, 7c, 8a, 8b, 8c, 10a, 10b, 10c, 11a, 11b, 11c, 12, 14 includes a known automatic valve. Further, an actuator for a switch such as a solenoid or a motor for actuating the valve is provided. As shown in FIG. 2, each of the on-off valves can be individually switched by being connected to the control device 20 constituting the purification system α and controlled by the control device 20. Control device 20 can include a computer.

Each of the first and second flow rate control valves 13 and 15 includes a flow rate adjusting actuator such as a motor for actuating the valve by including a known automatic valve. As shown in FIG. 2, each flow control valve can be individually controlled in flow rate by being connected to the control device 20 and controlled by the control device 20. Each of the first and second pressure regulating valves 26a and 26b includes a pressure adjusting actuator such as a motor for actuating the valve by including a known automatic valve. As shown in FIG. 2, each of the pressure regulating valves 26a and 26b can be individually controlled in pressure by being connected to the control device 20 and controlled by the control device 20.

The introduction pipe 3 is provided with a flow rate sensor 21 that detects the flow rate of the raw material carbon dioxide G1 supplied from the supply source, a buffer tank 22 that temporarily stores the raw material carbon dioxide G1, and a pressure sensor 23 for measuring the internal pressure of the buffer tank 22, The concentration sensor 24 for detecting the carbon dioxide concentration of the raw material carbon dioxide G1 and the third flow rate control valve 25 for adjusting the flow rate of the raw material carbon dioxide G1 introduced into each of the adsorption columns 2a, 2b, and 2c from the introduction pipe 3 are provided. The third flow rate control valve 25 includes a flow rate adjusting actuator such as a motor for actuating the valve by including a known automatic valve. As shown in FIG. 2, the flow sensor 21, the pressure sensor 23, the concentration sensor 24, and the third flow control valve 25 are connected to the control device 20. Further, the control device 20 is connected to a pressure sensor 27a that detects the internal pressure of each of the adsorption towers 2a, 2b, and 2c, 27b, 27c, an input device 28 such as a keyboard, and an output device 29 such as a display.

By temporarily storing the raw material carbon dioxide G1 in the buffer tank 22, the composition fluctuation of the raw material carbon dioxide G1 can be alleviated. Further, by controlling the third flow rate control valve 25 by the signal from the control device 20 to perform the flow rate adjustment operation, the flow rate of the raw material carbon dioxide G1 introduced into each of the adsorption columns 2a, 2b, and 2c is adjusted. Thereby, the flow rate of the raw material carbon dioxide G1 introduced into each of the adsorption towers 2a, 2b, and 2c is normally controlled so as to match the detected flow rate of the flow rate sensor 21. When the internal pressure of the buffer tank 22 measured by the pressure sensor 23 exceeds the upper limit set value, the raw material carbon dioxide G1 introduced into each of the adsorption towers 2a, 2b, and 2c is lowered in order to lower the internal pressure of the buffer tank 22. The flow rate is set to be larger than the detected flow rate of the flow sensor 21. When the internal pressure of the buffer tank 22 measured by the pressure sensor 23 is less than the lower limit set value, in order to increase the internal pressure of the buffer tank 22, the raw material carbon dioxide G1 introduced into each of the adsorption towers 2a, 2b, and 2c is The flow rate is set to be less than the detected flow rate of the flow sensor 21.

In order to purify the raw material carbon dioxide G1 by the purification system α, the raw material carbon dioxide is sequentially introduced into each of the adsorption towers 2a, 2b, and 2c, and the plurality of purifications are sequentially performed in each of the adsorption towers 2a, 2b, and 2c. The purification treatment cycle of the treatment step. As a plurality of purification treatment steps constituting one cycle of the purification treatment cycle, the following steps are sequentially performed: an adsorption step, a depressurization step, a depressurization pressure equalization step, a desorption step, a gas extrusion step, a pressure increasing pressure equalization step, and Boost step. The execution time of each purification treatment step may be determined and set in advance based on the purity or recovery rate of the purified gas G3 required. The execution timings of the purification processing steps in each of the adsorption columns 2a, 2b, and 2c are different from each other. Thereby, as shown in FIG. 3, in the adsorption device 1, the operation states (a) to (i) in which the purification treatment steps in the adsorption columns 2a, 2b, and 2c are different from each other are sequentially performed, and the carbon dioxide is continuously purified. . The arrows in Figure 3 indicate the direction of flow of the gas.

In order to sequentially perform the above-described purification processing step, the first to seventeenth on-off valves 6a, 6b, 6c, 7a, 7b, 7c, 8a, 8b, 8c, 10a, 10b, 10c, 11a, 11b, and the like are controlled by the control device 20. Each of 11c, 12, and 14 and each of the first and second flow control valves 13 and 15 are provided. Fig. 4 is a view showing the correspondence between the operation state (a) to (i), the purification processing steps performed in each of the adsorption towers 2a, 2b, and 2c, and the states of the first to the seventeenth on-off valves, and the symbol ○ Indicates the state in which the on-off valve is open, and the x symbol indicates the state in which the on-off valve is closed.

In the operating state (a), the first, fourth, eighth, eleventh, fifteenth, and sixteenth on-off valves 6a, 7a, 8b, 10b, 11c, and 12 are opened, and the remaining on-off valves are closed. The adsorption step is performed in the first adsorption tower 2a by opening the first and fourth on-off valves 6a and 7a. By opening the eighth, eleventh, fifteenth, and sixteenth on-off valves 8b, 10b, 11c, and 12, a gas extrusion step is performed in the second adsorption tower 2b, and a depressurization step is performed in the third adsorption tower 2c.

In the operating state (b), the first, fourth, eleventh, fifteenth, and sixteenth on-off valves 6a, 7a, 10b, 11c, and 12 are opened, and the remaining on-off valves are closed. By opening the first and fourth on-off valves 6a and 7a, the adsorption step is continued after the first adsorption tower 2a is relayed to the operation state (a). By opening the eleventh, fifteenth, and sixteenth on-off valves 10b, 11c, and 12, a pressure equalization step is performed in the second adsorption tower 2b, and a desorption pressure equalization step is performed in the third adsorption tower 2c.

In the operating state (c), the first, fourth, ninth, fourteenth, and seventeenth on-off valves 6a, 7a, 8c, 11b, and 14 are opened, and the remaining on-off valves are closed. By opening the first, fourth, fourteenth, and seventeenth on-off valves 6a, 7a, 11b, and 14, the adsorption step is continued after the first adsorption tower 2a is relayed to the operation state (b), and the second adsorption tower 2b is continued. The step of boosting is implemented. The desorption step is carried out in the third adsorption tower 2c by opening the ninth on-off valve 8c.

In the operating state (d), the second, fifth, ninth, twelfth, thirteenth, and sixteenth on-off valves 6b, 7b, 8c, 10c, 11a, and 12 are opened, and the remaining on-off valves are closed. The adsorption step is performed in the second adsorption tower 2b by opening the second and fifth on-off valves 6b and 7b. By opening the ninth, twelfth, thirteenth, and sixteenth on-off valves 8c, 10c, 11a, and 12, a pressure reduction step is performed in the first adsorption tower 2a, and a gas extrusion step is performed in the third adsorption tower 2c.

In the operating state (e), the second, fifth, twelfth, thirteenth, and sixteenth on-off valves 6b, 7b, 10c, 11a, and 12 are opened, and the remaining on-off valves are closed. By opening the second and fifth on-off valves 6b and 7b, the adsorption step is continued after the second adsorption tower 2b is in the relay operation state (d). By opening the 12th, 13th, and 16th on-off valves 10c, 11a, and 12, the desorption depressing step is performed in the first adsorption tower 2a, and the boosting pressure equalization step is performed in the third adsorption tower 2c.

In the operating state (f), the second, fifth, seventh, fifteenth, and seventeenth on-off valves 6b, 7b, 8a, 11c, and 14 are opened, and the remaining on-off valves are closed. By opening the second, fifth, fifteenth, and seventeenth on-off valves 6b, 7b, 11c, and 14, the adsorption step is continued after the second adsorption tower 2b is in the relay operation state (e), and the third adsorption tower 2c is applied to the third adsorption tower 2c. The step of boosting is implemented. The desorption step is carried out in the first adsorption tower 2a by opening the seventh on-off valve 8a.

In the operating state (g), the third, sixth, seventh, tenth, fourteenth, and sixteenth on-off valves 6c, 7c, 8a, 10a, 11b, and 12 are opened, and the remaining on-off valves are closed. The adsorption step is performed in the third adsorption tower 2c by opening the third and sixth on-off valves 6c and 7c. By opening the seventh, tenth, fourteenth, and sixteenth on-off valves 8a, 10a, 11b, and 12, a gas extrusion step is performed in the first adsorption tower 2a, and a pressure reduction step is performed in the second adsorption tower 2b.

In the operating state (h), the third, sixth, tenth, fourteenth, and sixteenth on-off valves 6c, 7c, 10a, 11b, and 12 are opened, and the remaining on-off valves are closed. By opening the third and sixth on-off valves 6c and 7c, the adsorption step is continued after the third adsorption tower 2c relays the operation state (g). By opening the tenth, fourteenth, and sixteenth on-off valves 10a, 11b, and 12, a pressure equalization step is performed in the first adsorption tower 2a, and a desorption pressure equalization step is performed in the second adsorption tower 2b.

In the operating state (i), the third, sixth, eighth, thirteenth, and seventeenth on-off valves 6c, 7c, 8b, 11a, and 14 are opened, and the remaining on-off valves are closed. By opening the third, sixth, thirteenth, and seventeenth on-off valves 6c, 7c, 11a, and 14, the step of boosting is performed in the first adsorption tower 2a, and the operation is performed in the third adsorption tower 2c (h). The adsorption step is then continued. The desorption step is carried out in the second adsorption tower 2b by opening the eighth on-off valve 8b.

When the adsorption step is performed in any of the adsorption towers 2a, 2b, and 2c, the raw material carbon dioxide G1 is introduced into the adsorption tower through the introduction flow path. The inside of the adsorption column is pressurized to the adsorption pressure required in the adsorption step by the pressure of the raw material carbon dioxide G1. Therefore, the carbon dioxide contained in the introduced raw material carbon dioxide G1 is adsorbed to the adsorption under pressure. Agent. Further, the impurity gas which is not adsorbed by the adsorbent is discharged as the outgas G2 from the inside of the adsorption tower via the escape flow path.

When the pressure reduction step is performed in any of the adsorption towers 2a, 2b, and 2c, the inside of the adsorption tower is connected to the inside of the adsorption towers 2a, 2b, and 2c of the gas extrusion step via the communication passage. The purified gas flow path leads to the atmospheric pressure space, and the pressure gradually decreases to become the first intermediate pressure between the adsorption pressure and the atmospheric pressure. At this time, the internal gas G4 of the adsorption tower in the depressurization step is introduced into the adsorption tower in the gas extrusion step. The reduction in the internal pressure of the adsorption column in the depressurization step corresponds to the amount of gas introduced into the adsorption column in the gas extrusion step.

When the desorption step of desorption is performed in any of the adsorption towers 2a, 2b, and 2c, the inside of the adsorption tower is connected to the adsorption towers 2a, 2b, and 2c for performing the pressure equalization step through the communication passage. In either case, the pressure is reduced to become the second intermediate pressure between the first intermediate pressure and the atmospheric pressure. At this time, the internal gas G5 of the adsorption tower in the depressurization pressure equalization step is introduced into the adsorption tower in the pressure equalization step. Since the inside of the adsorption tower in the depressurization pressure equalization step and the inside of the adsorption tower in the pressure equalization pressure increasing step are equalized, the internal pressure of the adsorption tower in the pressure equalization pressure increasing step is increased to be equal to the second intermediate pressure. In other words, the adsorption tower 2a in the state of any one of the adsorption towers 2a, 2b, 2c in a state after the gas extrusion step and before the pressure increase step, and after the pressure reduction step and before the desorption step can be used. The inside of any of 2b and 2c is connected to the same pressure, and is pressurized in any one of the adsorption towers 2a, 2b, and 2c in a state after the gas extrusion step and before the pressure increasing step. The pressure equalization step is carried out, and the pressure equalization step for desorption is carried out in any of the adsorption towers 2a, 2b, 2c in a state after the pressure reduction step and before the desorption step.

When the desorption step is performed in any of the adsorption towers 2a, 2b, and 2c, the inside of the adsorption tower is led to the normal pressure space via the purification gas flow path, and the pressure is adjusted by the second pressure regulating valve 26b. At the end of the depressurization pressure equalization step, the pressure is gradually reduced, and the pressure is reduced to The pressure required in the desorption step is desorbed from the adsorbent. The desorbed carbon dioxide is discharged as a purified gas G3 from the inside of the adsorption tower through the purified gas flow path. The pressure inside the adsorption tower at the end of the desorption step is such that the purified gas G3 flows in the purification gas flow path due to its own pressure and is discharged to the normal pressure space in the desorption step, and becomes a pressure slightly higher than the atmospheric pressure.

At the time when the desorption step is completed, even if the inside of the adsorption tower is connected to the atmospheric pressure space, the flow path resistance of the purified gas flow path or the like is present, and thus the inside of the adsorption tower is retained with high-purity carbon dioxide desorbed from the adsorbent.

When the pressure increasing step is performed in any of the adsorption towers 2a, 2b, and 2c, the inside of the adsorption tower leads to the inside of the adsorption towers 2a, 2b, and 2c in which the adsorption step is performed via the communication passage. At this time, by introducing a portion of the outgas G2 discharged from the adsorption column for performing the adsorption step into the adsorption column in the step of increasing pressure, the inside of the adsorption column in the step of increasing pressure is pressurized to raise the pressure to adsorption. Pressure or adsorption pressure nearby.

When the gas extrusion step is performed in any one of the adsorption towers 2a, 2b, and 2c, the adsorption tower is in a state after the desorption step and before the pressure increase step. The inside of any one of the adsorption towers 2a, 2b, and 2c in a state after the desorption step and before the pressure-up step is passed to the adsorption towers 2a, 2b, and 2c in the depressurization step via the communication passage. The inside of the person, in turn, leads to the atmospheric space via the purified gas flow path. Thus, any one of the adsorption columns 2a, 2b, 2c in the depressurization step can be introduced into any of the adsorption columns 2a, 2b, 2c in a state after the desorption step and before the pressure increasing step. The internal gas G4 is a gas pressure which is externally extruded through the purified gas flow path by the carbon dioxide inside the adsorption towers 2a, 2b, and 2c which are in the state after the desorption step and before the pressure increasing step. Step out. The carbon dioxide extruded in the gas extrusion step is recovered as the purified gas G3'. Further, in the case where carbon dioxide desorbed from the adsorbent is present during the gas extrusion step, the carbon dioxide may be extruded and recovered.

In the gas extrusion step, the pressure is reduced to any one of the adsorption towers 2a, 2b, and 2c. The amount of gas introduced by any of the adsorption columns 2a, 2b, and 2c in the step is changed in accordance with the change in the concentration of carbon dioxide in the raw material carbon dioxide G1. That is, when the carbon dioxide concentration of the raw material carbon dioxide G1 is increased, the amount of the gas is increased, and if the concentration of the carbon dioxide is lowered, the amount of the gas is decreased, thereby optimizing. Therefore, as described below, the execution time of the gas extrusion step is made constant, and the flow rate of the gas flowing through the communication passage is adjusted by the first flow rate control valve 13.

In the gas extrusion step, in order to introduce the internal gas of any one of the adsorption towers 2a, 2b, and 2c in the depressurization step into any one of the adsorption towers 2a, 2b, and 2c, the switch of the flow path is opened. Any of the valves. Therefore, the amount of gas introduced into any one of the adsorption towers 2a, 2b, and 2c in the gas extrusion step corresponds to the product of the execution time of the gas extrusion step and the gas flow rate flowing through the communication passage. The execution time of the gas pressing step of the present embodiment is set to a predetermined predetermined time, and the constant execution time is stored in the control device 20.

Further, in the gas extrusion step, the amount of gas introduced into any one of the adsorption towers 2a, 2b, and 2c can be changed by adjusting the flow rate of the gas flowing through the communication passage by the first flow rate control valve 13. Therefore, in the gas extrusion step, when the internal gas G4 of any one of the adsorption towers 2a, 2b, and 2c in the depressurization step is introduced into any one of the adsorption towers 2a, 2b, and 2c, the communication flow path is introduced. The predetermined correspondence between the flow rate of the gas flowing in the medium and the concentration of carbon dioxide in the raw material carbon dioxide G1 is stored in the control device 20.

The adsorption tower 2a which is in the decompression step from any one of the adsorption towers 2a, 2b, 2c in the gas extrusion step is changed in accordance with the change in the carbon dioxide concentration of the raw material carbon dioxide G1 measured by the concentration sensor 24 In the method of introducing the amount of gas introduced by any of 2b and 2c, in order to perform the gas pressing step by the execution time stored in the control device 20, the on-off valve is controlled, and the first use is changed based on the stored correspondence relationship. The flow rate of the flow control valve 13 is adjusted.

In this case, the amount of gas introduced into any one of the adsorption columns 2a, 2b, 2c in the gas extrusion step and the internal pressure at the start of the gas extrusion step in the adsorption column in the depressurization step are The pressure difference of the internal pressure at the end of the gas extrusion step corresponds. When the pressure difference is δ MPa, the carbon dioxide concentration of the raw material carbon dioxide G1 is ε vol%, A and B are set to be constant, and the internal pressure of the adsorption tower in the depressurization step is decreased according to δ=A ε ^{B .} The obtained pressure difference δ may be optimized for the amount of gas introduced from any of the adsorption towers 2a, 2b, and 2c in the gas extrusion step. Here, the values of the constant A and the constant B are preferably set to be in the range of 3.115 × 10 ^-5 ≧A ≧ 7.15 × 10 ^-6 and 1.97 ≦ B ≦ 2.249. In other words, the gas flow rate and the raw material carbon dioxide which are adjusted in the communication flow path adjusted by the first flow rate control valve 13 are determined in advance by the experiment so that the pressure difference is δ MPa for a certain period of time during which the gas extrusion step is performed. The relationship between the carbon dioxide concentration of G1 is sufficient. The adjustment of the gas flow rate by the first flow rate control valve 13 may be performed once in one cycle of the purification treatment step. However, if the concentration variation of the raw material carbon dioxide G1 is small, it may be performed once in a plurality of cycles.

Any one of the adsorption towers 2a, 2b, 2c which is in the depressurization step from any one of the adsorption towers 2a, 2b, 2c in the gas extrusion step in accordance with the change in the carbon dioxide concentration in the raw material carbon dioxide G1. In the case of the amount of gas to be introduced, the pressure at the point where the inside of the adsorption column in the pressure equalization step of pressure increase and the inside of the adsorption column in the pressure equalization step for desorption are equalized are changed. Therefore, when the internal pressure of the adsorption column in the step of increasing pressure is increased to the adsorption pressure, it is preferred that the amount of the outgas G2 introduced from the adsorption column in the adsorption step to the adsorption column in the pressure increasing step also changes. . In this case, in the step of boosting, the time of the step of increasing the pressure is set to a predetermined constant value, and the flow rate of the gas flowing through the communication channel may be adjusted by the second flow rate control valve 15. Therefore, the relationship between the flow rate of the gas flowing through the communication flow path and the carbon dioxide concentration of the raw material carbon dioxide G1 adjusted by the second flow rate control valve 15 can be determined in advance by experiments.

The change from the change in the carbon dioxide concentration of the raw material carbon dioxide G1 to the suction step 2a, 2b, 2c in the gas depressing step is carried out in the depressurization step. The variation of the amount of gas introduced by any of the additional towers 2a, 2b, and 2c may also adjust the implementation time of the gas extrusion step. In this case, it is not necessary to use the flow rate control by the first flow rate control valve 13.

That is, the amount of gas introduced into any one of the adsorption towers 2a, 2b, and 2c in the gas extrusion step and the execution time of the gas extrusion step and the gas flow rate in the communication flow path Since the product corresponds to each other, the amount of gas can be changed by adjusting the execution time of the gas pressing step.

Therefore, the predetermined correspondence relationship between the execution time of the gas pressing step and the carbon dioxide concentration of the raw material carbon dioxide G1 is stored in the control device 20. The gas introduced from any one of the adsorption towers 2a, 2b, and 2c in the gas extrusion step is changed in accordance with the change in the carbon dioxide concentration of the raw material carbon dioxide G1 measured by the concentration sensor 24 In the manner of the amount, the execution time of the gas pressing step, that is, the switching valve control time for the gas pressing step, is changed based on the correspondence relationship stored in the control device 20. Further, when the execution time of the gas pressing step is changed, the time for implementing the pressure increasing and desorbing steps is changed without changing the time of the adsorption step. For example, when the adsorption time in the first adsorption tower 2a under the operation states (a) to (c) is not changed, and the execution time of the gas extrusion step in the operation state (a) is changed, the operation state is changed. (c) The implementation time of the step of boosting and desorbing can be performed. Others may be controlled in the same manner as in the embodiment.

According to the above-described embodiment and the modification, the adsorption tower which is in the depressurization step is introduced into any one of the adsorption towers 2a, 2b, and 2c in a state after the desorption step and before the pressure increasing step by performing the gas extrusion step. The internal gas of any of the other gases is used to press the high-purity carbon dioxide remaining in the inside of the adsorption tower after the desorption step to the outside. Therefore, it is possible to avoid the waste and recover the carbon dioxide of high purity which is extruded, and to increase the recovery rate of carbon dioxide, thereby obtaining carbon dioxide having a purity of 95 vol% or more at a recovery rate of 90% or more.

Further, when the carbon dioxide concentration of the raw material carbon dioxide G1 is increased, the gas introduced into any one of the adsorption towers 2a, 2b, and 2c in the gas extrusion step is added. When the carbon dioxide concentration in the raw material carbon dioxide G1 is decreased, the amount of the introduced gas is reduced, whereby the purity variation of the carbon dioxide extruded in the gas extrusion step can be suppressed, and the purity of the recovered carbon dioxide can be stabilized, for example, 85. A higher recovery ratio of more than % yields a quality-stable carbon dioxide having a purity of 97 vol% or more. The carbon dioxide having a purity of 97 vol% or more can be used by mixing with the raw material gas supplied to the liquefaction apparatus, and the load on the liquefaction apparatus can be reduced.

Further, the adsorption tower in the pressure equalization step is pressurized by feeding the internal gas of the adsorption tower in the depressurization pressure equalization step, and the carbon dioxide contained in the supplied gas is followed by the adsorption step. It is adsorbed to the adsorbent. Thereby, the recovery rate of carbon dioxide can be improved.

Further, since the inside of the adsorption tower is pressurized to the adsorption pressure by the pressure of the raw material carbon dioxide G1, it is not necessary to provide a dedicated device for pressurization or decompression, and the power cost, the maintenance cost, and the like can be reduced, and since there is no vacuum operation, Therefore, air or the like is not mixed from the outside, so it is related to the maintenance of quality. That is, it is practical to use the pressure of the raw material carbon dioxide.

Fig. 5 is a view showing another pressure swing type adsorption device 100 different from the above-described pressure swing type adsorption device 1. The adsorption device 100 is different from the adsorption device 1 in that the third communication portion 9c, the sixteenth on-off valve 12, the first flow rate control valve 13, the second flow rate control valve 15, and the concentration sensor 24 are not provided. The other components of the adsorption device 100 are the same as those of the above-described adsorption device 1, and the same portions are denoted by reference numerals, and the description of the same portions is omitted.

Fig. 6 and Fig. 7 show a method for purifying carbon dioxide in a comparative example using the adsorption device 100 shown in Fig. 5. Hereinafter, differences from the above-described embodiment will be described, and the description of the same portions will be omitted.

In the comparative example, as the purification treatment step, the adsorption step, the depressurization pressure equalization step, the desorption step, the pressure increasing pressure equalization step, and the pressure increasing step are sequentially performed without performing the pressure reduction step and the gas pressure in the embodiment. Step out. Therefore, as shown in FIG. 6, the suction is sequentially performed. The operation steps (a) '~(f)' in which the purification processing steps in each of the towers 2a, 2b, and 2c are different from each other.

In the comparative example, the first to fifteenth and seventeenth on-off valves 6a, 6b, 6c, 7a, 7b, 7c, 8a, 8b, 8c, 10a, 10b are controlled by the control device 20 in order to sequentially perform the purification treatment step. , 10c, 11a, 11b, 11c, 14 each. Fig. 7 shows the operation state (a) '~(f)', the purification processing steps performed in each of the adsorption towers 2a, 2b, and 2c, and the states of the first to the fifteenth and seventeenth on-off valves. Corresponding relationship, the symbol ○ indicates the state in which the on-off valve is open, and the symbol x indicates the state in which the on-off valve is closed.

In the operating state (a)', the first, fourth, eleventh, and twelfth, on-off valves 6a, 7a, 10b, and 10c are opened, and the remaining on-off valves are closed. The adsorption step is performed in the first adsorption tower 2a by opening the first and fourth on-off valves 6a and 7a. By opening the eleventh and twelfth on-off valves 10b and 10c, a step of pressure equalization is performed in the second adsorption tower 2b, and a pressure equalization step for desorption is performed in the third adsorption tower 2c.

In the operating state (b)', the first, fourth, ninth, fourteenth, and seventeenth on-off valves 6a, 7a, 8c, 11b, and 14 are opened, and the remaining on-off valves are closed. By opening the first, fourth, fifteenth, and seventeenth on-off valves 6a, 7a, 11b, and 14, the adsorption step is continued after the first adsorption tower 2a is relayed to the operation state (a)', and the second adsorption tower is operated. The boosting step is implemented in 2b. The desorption step is carried out in the third adsorption tower 2c by opening the ninth on-off valve 8c.

In the operating state (c)', the second, fifth, tenth, and twelfth switching valves 6b, 7b, 10a, and 10c are opened, and the remaining switching valves are closed. The adsorption step is performed in the second adsorption tower 2b by opening the second and fifth on-off valves 6b and 7b. By opening the tenth and twelfth on-off valves 10a and 10c, the desorption depressing step is performed in the first adsorption tower 2a, and the step-up pressure equalization step is performed in the third adsorption tower 2c.

In the operating state (d)', the second, fifth, seventh, fifteenth, and seventeenth on-off valves 6b, 7b, 8a, 11c, and 14 are opened, and the remaining on-off valves are closed. After the second, fifth, fifteenth, and seventeenth on-off valves 6b, 7b, 11c, and 14 are opened, the second adsorption tower 2b is relayed to the operation state (c)'. The adsorption step is continued, and a pressure increasing step is performed in the third adsorption column 2c. The desorption step is carried out in the first adsorption tower 2a by opening the seventh on-off valve 8a.

In the operating state (e)', the third, sixth, tenth, and eleventh on-off valves 6c, 7c, 10a, and 10b are opened, and the remaining on-off valves are closed. The adsorption step is performed in the third adsorption tower 2c by opening the third and sixth on-off valves 6c and 7c. By opening the tenth and eleventh on-off valves 10a and 10b, a pressure equalization step is performed in the first adsorption tower 2a, and a desorption pressure equalization step is performed in the second adsorption tower 2b.

In the operating state (f)', the third, sixth, eighth, thirteenth, and seventeenth on-off valves 6c, 7c, 8b, 11a, and 14 are opened, and the remaining on-off valves are closed. By opening the third, sixth, thirteenth, and seventeenth on-off valves 6c, 7c, 11a, and 14 , a step of boosting is performed in the first adsorption tower 2a in the step of boosting, and relaying is performed in the third adsorption tower 2c. The adsorption step is continued after the operation state (e)'. The desorption step is carried out in the second adsorption tower 2b by opening the eighth on-off valve 8b.

In the comparative example, the adsorption step, the depressurization pressure equalization step, the desorption step, the pressure increasing pressure equalization step, and the pressure increasing step were carried out in the same manner as in the above embodiment. When the desorption step of desorption is performed in any of the adsorption towers 2a, 2b, and 2c, the inside of the adsorption tower is connected to the adsorption towers 2a, 2b, and 2c for performing the pressure equalization step through the communication passage. In either case, the pressure is reduced to become an intermediate pressure between the adsorption pressure and the atmospheric pressure. At this time, the internal gas G5 of the adsorption tower in the depressurization pressure equalization step is introduced into the adsorption tower in the pressure equalization step. Since the inside of the adsorption tower in the depressurization pressure equalization step and the inside of the adsorption tower in the pressure increasing pressure equalization step are equalized, the internal pressure of the adsorption tower in the pressure increasing pressure equalization step rises to be equal to the intermediate pressure.

Since the gas extrusion step is not carried out in the above comparative example, high-purity carbon dioxide retention from the adsorbent is desorbed in any of the adsorption towers 2a, 2b, and 2c in a state after the desorption step and before the pressure-up step. Inside it. The retained high-purity carbon dioxide is partially adsorbed to the adsorbent in the subsequent adsorption step, but the remainder is discharged as the outgas from the adsorption towers 2a, 2b, 2c, so that the recovery rate of carbon dioxide is lowered.

[Examples] [Example 1]

The raw material carbon dioxide G1 was purified by using the adsorption device 1 shown in Fig. 1 in accordance with the above embodiment.

The raw material carbon dioxide G1 contained 75 vol% of carbon dioxide, and contained 18.3 vol% of hydrogen as an impurity gas, 4.7 vol% of nitrogen, 1.6 vol% of argon, and 0.4 vol% of methane.

The supply flow rate of the raw material carbon dioxide G1 to the adsorption device 1 was set to 7.6 NL/min.

Each of the adsorption towers 2a, 2b, and 2c has a cylindrical shape having an inner diameter of 37.1 mm and an inner dimension of 1000 mm.

To each of the adsorption columns 2a, 2b, and 2c, 1.08 liter of a carbon molecular sieve was filled as an adsorbent.

As a purification treatment step, the adsorption step was carried out in sequence: 210 seconds of adsorption, 40 seconds of depressurization, 15 seconds of desorption for desorption, 155 seconds of desorption, 40 seconds of gas extrusion, and 15 seconds of pressure equalization Press the step for 155 seconds.

The internal pressure (adsorption pressure) of the adsorption towers 2a, 2b, and 2c in the adsorption step was set to 0.8 MPa (gauge pressure). The internal pressure (first intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization step was set to 0.68 MPa (gauge pressure). The internal pressure (second intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization pressure equalization step was set to 0.32 MPa (gauge pressure). The internal pressure of the adsorption towers 2a, 2b, 2c at the end of the desorption step was set to 0.05 MPa (gauge pressure).

The purified gas G3 and G3' obtained had a carbon dioxide concentration of 95 vol%, and the recovery was 91%.

[Embodiment 2]

The raw material carbon dioxide G1 was purified by using the adsorption device 1 shown in Fig. 1 in accordance with the above embodiment.

The raw material carbon dioxide G1 contained 82 vol% of carbon dioxide, and contained 11.3 vol% of hydrogen as an impurity gas, 4.7 vol% of nitrogen, 1.6 vol% of argon, and 0.4 vol% of methane.

For purification, the adsorption step was 180 seconds, the depressurization step was 40 seconds, the desorption depressing step was 15 seconds, the desorption step was 125 seconds, the gas extrusion step was 40 seconds, the pressure increasing step was 15 seconds, and the pressure increasing step was performed. 125 seconds.

The internal pressure (adsorption pressure) of the adsorption towers 2a, 2b, and 2c in the adsorption step was set to 0.8 MPa (gauge pressure). The internal pressure (first intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization step was set to 0.65 MPa (gauge pressure). The internal pressure (second intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization pressure equalization step was set to 0.3 MPa (gauge pressure). The internal pressure of the adsorption towers 2a, 2b, 2c at the end of the desorption step was set to 0.05 MPa (gauge pressure).

Other conditions are the same as in the first embodiment.

The obtained purified gas G3, G3' had a carbon dioxide concentration of 97.0 vol%, and the recovery was 85%.

[Example 3]

The raw material carbon dioxide G1 was purified by using the adsorption device 1 shown in Fig. 1 in accordance with the above embodiment.

For purification, the adsorption step was 180 seconds, the depressurization step was 40 seconds, the desorption depressing step was 15 seconds, the desorption step was 125 seconds, the gas extrusion step was 40 seconds, the pressure increasing step was 15 seconds, and the pressure increasing step was performed. 125 seconds.

The internal pressure (adsorption pressure) of the adsorption towers 2a, 2b, and 2c in the adsorption step was set to 0.8 MPa (gauge pressure). The internal pressure (first intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the pressure reduction step was set to 0.5 MPa (gauge pressure). The internal pressure (second intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization pressure equalization step was set to 0.22 MPa (gauge pressure). The internal pressure of the adsorption towers 2a, 2b, 2c at the end of the desorption step was set to 0.05 MPa (gauge pressure).

Other conditions are the same as in the first embodiment.

The obtained purified gas G3, G3' has a carbon dioxide concentration of 92.0 vol%, and the recovery rate It is 91%.

[Example 4]

For purification, the adsorption step was 180 seconds, the depressurization step was 40 seconds, the desorption depressing step was 15 seconds, the desorption step was 125 seconds, the gas extrusion step was 40 seconds, the pressure increasing step was 15 seconds, and the pressure increasing step was performed. 125 seconds.

The internal pressure (adsorption pressure) of the adsorption towers 2a, 2b, and 2c in the adsorption step was set to 0.8 MPa (gauge pressure). The internal pressure (first intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization step was set to 0.75 MPa (gauge pressure). The internal pressure (second intermediate pressure) of the adsorption towers 2a, 2b, and 2c at the end of the depressurization pressure equalization step was set to 0.35 MPa (gauge pressure). The internal pressure of the adsorption towers 2a, 2b, 2c at the end of the desorption step was set to 0.05 MPa (gauge pressure).

Other conditions are the same as in the first embodiment.

The obtained purified gas G3 and G3' had a carbon dioxide concentration of 95.0 vol%, and the recovery was 87%.

[Comparative Example 1]

The raw material carbon dioxide G1 was purified using the adsorption device 100 shown in Fig. 5 .

As the purification treatment step, the adsorption step, the depressurization pressure equalization step, the desorption step, the pressure increase pressure equalization step, and the pressure increase step are carried out in sequence, and the pressure reduction step and the gas pressure extraction step are not performed.

The adsorption step was 170 seconds, the desorption depressurization step was 15 seconds, the desorption step was 155 seconds, the boosting pressure equalization step was 15 seconds, and the pressure increasing step was 155 seconds.

Other conditions are the same as in the first embodiment.

The purified gas G3 obtained had a carbon dioxide concentration of 89 vol% and a recovery of 84%.

As shown in the following Table 1, it was confirmed that high-purity carbon dioxide can be obtained without lowering the recovery rate according to the examples as compared with the comparative examples.

The present invention is not limited to the above embodiments, examples, and modifications. For example, as the purification treatment step, the depressurization pressure equalization step and the pressure increase pressure equalization step are not essential, and the desorption step may be performed after the depressurization step, and the pressure increasing step may be performed after the gas extrusion step. Further, the number of adsorption columns in the adsorption device is not limited to three, and may be plural.

Claims (8)

A method for purifying carbon dioxide by using a pressure swing type adsorption device having a plurality of adsorption columns to purify a raw material carbon dioxide containing an impurity gas, and absorbing an adsorbent which adsorbs carbon dioxide preferentially with an impurity gas into each of the adsorption towers The raw material carbon dioxide is sequentially introduced into each of the adsorption towers, and in each of the adsorption towers, a step of adsorbing carbon dioxide contained in the introduced raw material carbon dioxide under pressure is sequentially performed. The adsorbent, and the impurity gas not adsorbed by the adsorbent is discharged as an outgas; the depressurization step is to reduce the internal pressure; the desorption step is to desorb and discharge the carbon dioxide from the adsorbent; and the step of pressurizing And the method of recovering the internal pressure by the carbon dioxide discharged from the adsorption towers in the desorption step, wherein the carbon dioxide purification method is characterized in that the gas extrusion step is performed by Said to the state after the desorption step and before the step of boosting In any one of the towers, the internal gas of any one of the adsorption towers in the depressurization step is introduced, and the adsorption tower is retained in the state after the desorption step and before the pressure increasing step. The carbon dioxide inside is pressurized to the outside, and the carbon dioxide extruded in the above gas extrusion step is recovered as a purified gas. The method for purifying carbon dioxide according to claim 1, wherein the adsorption tower is changed from the gas extraction step to the adsorption column in any one of the adsorption columns from the pressure reduction step. The amount of gas introduced by either of them. The method for purifying carbon dioxide according to claim 1, wherein the inside of the adsorption tower in a state after the gas extrusion step and before the pressure increasing step is desorbed after the decompression step and the desorption step The inside of any one of the adsorption towers in the state before the step is connected in an equal pressure manner, and is carried out in any of the adsorption towers in a state after the gas pressing step and before the pressure increasing step. The pressure equalization step is carried out, and the desorption step for desorption is carried out in any of the adsorption towers in the state after the above-mentioned decompression step and before the desorption step. The method for purifying carbon dioxide according to claim 2, wherein the inside of the adsorption tower in a state after the gas extrusion step and before the pressure increasing step is desorbed after the decompression step and the desorption step The inside of any one of the adsorption towers in the state before the step is connected in an equal pressure manner, and is carried out in any of the adsorption towers in a state after the gas pressing step and before the pressure increasing step. The pressure equalization step is carried out, and the desorption step for desorption is carried out in any of the adsorption towers in the state after the above-mentioned decompression step and before the desorption step. The method for purifying carbon dioxide according to any one of claims 1 to 4, wherein a compressed gas is used as the raw material carbon dioxide, and the inside of the adsorption tower is pressurized to the adsorption pressure required in the adsorption step by the pressure of the raw material carbon dioxide. The pressure required to be decompressed in the desorption step is reduced by connecting the inside of the adsorption tower to the atmospheric pressure space. A carbon dioxide purification system comprising a pressure swing adsorption device for purifying a raw material carbon dioxide containing an impurity gas, wherein the pressure swing adsorption device has a plurality of adsorption towers that store an adsorbent that adsorbs carbon dioxide in preference to an impurity gas. And an introduction flow path for introducing the raw material carbon dioxide into each of the adsorption towers; an escape flow path for discharging the outgas from the adsorption towers; and a purification gas flow path, which is used for Discharging carbon dioxide from each of the adsorption towers; communicating a flow path for communicating any one of the adsorption towers with any one of the other; introducing an on-off valve that connects the adsorption towers to the introduction flow Each of the roads is opened and closed individually; the gas circuit switching valve is separately opened and closed between the adsorption towers and the air flow passage; the purified gas circuit switching valve is configured by the above adsorption towers and the above Individually opening and closing the purified gas flow paths; and connecting the on-off valves, which open the respective adsorption towers and the communication flow paths individually Each of the above-described switching valves is an automatic valve having a switching actuator that can be individually switched, and is connected to a control device, and the above-described control is performed in each of the adsorption towers in the following steps. The apparatus controls the above-mentioned respective on-off valves: an adsorption step of adsorbing carbon dioxide contained in the introduced raw material carbon dioxide to the adsorbent under pressure, and discharging the impurity gas not adsorbed by the adsorbent as an outgas a depressurization step for reducing internal pressure; a desorption step for desorbing and discharging carbon dioxide from the adsorbent; and a step of increasing the internal pressure; the carbon dioxide purification system is characterized by: The above-described switching valves are controlled by the above-described control device in such a manner that the gas is pushed out by any one of the adsorption towers in a state after the desorption step and before the pressure increasing step. Introducing the internal gas of any of the above adsorption towers in the above-mentioned decompression step, and staying in Following the above and the carbon dioxide inside the desorption step of the adsorption tower according to any of the above-described state before the step of boosting the pressure of the one to the outside. A purification system for carbon dioxide according to claim 6, further comprising: a flow rate control valve that regulates a flow rate of the gas flowing through the communication passage; the flow rate control valve has a flow rate adjustment actuator so as to perform a flow rate adjustment operation The automatic valve is connected to the control device, and includes a sensor for detecting a concentration of carbon dioxide in the raw material carbon dioxide and connected to the control device, and a predetermined execution time of the gas pressing step is stored in the control device. In the gas extrusion step, the flow rate of the gas flowing through the communication passage when the internal gas of the adsorption tower in the depressurization step is introduced into any one of the adsorption towers, and the raw material The predetermined correspondence relationship between the carbon dioxide concentrations in the carbon dioxide is stored in the control device, and is changed to the adsorption tower according to the change in the carbon dioxide concentration detected by the sensor. One of the above adsorption towers in the above-mentioned decompression step In order to perform the gas pressing step by performing the gas pressing step by the execution time stored in the control device, the switching valve is controlled to change the flow rate of the regulating gas of the flow rate control valve based on the correspondence relationship. A purification system for carbon dioxide according to claim 6, comprising: a sensor for detecting a carbon dioxide concentration of the carbon dioxide of the raw material and connected to the control device, wherein an execution time of the gas pressing step and a carbon dioxide concentration in the raw material carbon dioxide The predetermined correspondence relationship is stored in the control device, and is changed to any one of the adsorption towers in the gas extrusion step according to a change in the carbon dioxide concentration detected by the sensor. In the method of introducing the amount of gas, the execution time of the gas pressing step is changed based on the correspondence relationship by the control device.