JP6855525B2 - How to make carbon dioxide - Google Patents

Description

The present disclosure relates to a carbon dioxide producing apparatus and a carbon dioxide producing method.

A technique for recovering carbon dioxide from exhaust gas emitted from combustion equipment such as a boiler is known. As such a technique, a chemical absorption method using an aqueous amine solution or the like is used. In the chemical absorption method, the amine aqueous solution and the mixed gas are brought into contact with each other in the absorption tower to absorb carbon dioxide in the amine aqueous solution. The amine aqueous solution that has absorbed the carbon dioxide is heated in a regeneration tower to release carbon dioxide, and the carbon dioxide and the amine aqueous solution are separated. In this way, the carbon dioxide-containing gas containing a high concentration of carbon dioxide is recovered while circulating the amine aqueous solution.

The carbon dioxide-containing gas recovered by such a method contains various trace components (impurities) other than carbon dioxide depending on the properties of the fuel gas. Patent Document 1 proposes to reduce impurities in carbon dioxide-containing gas by providing a reduction treatment device containing a reduction catalyst and an adsorption treatment device containing activated carbon on the downstream side of the regeneration tower. ..

Japanese Unexamined Patent Publication No. 2016-188161

When reducing impurities by using a reduction catalyst and an adsorbent such as activated carbon, it is necessary to replace them regularly. Of these, the adsorbent has the property of adsorbing water and the like, so in order to exhibit its original performance, it is necessary to perform work to reduce the water content by drying after filling the adsorption tower. During this work, the adsorption tower cannot be used to reduce impurities and high-purity carbon dioxide cannot be produced, so that the work is required to be shortened as much as possible.

Therefore, the present disclosure provides a method for producing carbon dioxide that can reduce the production loss of high-purity carbon dioxide. The present disclosure provides a carbon dioxide production apparatus capable of reducing the production loss of high-purity carbon dioxide.

The method for producing carbon dioxide according to one aspect of the present disclosure is a method for producing carbon dioxide using a plurality of adsorption towers containing an adsorbent that adsorbs impurities of a raw material gas containing carbon dioxide, and adsorbs at least one of them. While continuing the production of carbon dioxide using the tower, the adsorbent filled in the adsorption tower different from the adsorption tower is dried using a part of the purified gas obtained by reducing impurities from the raw material gas. Has a drying process.

In this production method, purified gas is used to dry the adsorbent filled in the adsorption tower. Since the production of carbon dioxide can be carried out in parallel using at least one adsorption tower during the drying process, it is not necessary to stop the production of carbon dioxide. Therefore, the production loss of high-purity carbon dioxide can be reduced.

In the drying step, it is preferable to heat the purified gas and then supply the purified gas to an adsorption tower filled with an adsorbent. By supplying the heated purified gas to the adsorption tower, the adsorbent can be quickly dried. Therefore, the drying process can be shortened.

The plurality of adsorption towers in the above manufacturing method may have a first adsorption tower and a second adsorption tower connected so that the raw material gas sequentially flows. In this case, the above-mentioned production method includes a stop step of taking out the used adsorbent of the first adsorption tower from which the introduction of the raw material gas is stopped while continuing the production of carbon dioxide in the second adsorption tower, and the unused adsorbent. A drying step of supplying a part of carbon dioxide derived from the second adsorption tower to the filled first adsorption tower as a part of the purified gas to dry the unused adsorbent, and after drying the unused adsorbent. , It is preferable to have an operation start step of obtaining carbon dioxide from the first adsorption tower.

In the above manufacturing method, while continuing the production of carbon dioxide in the second adsorption tower, the stop step, the drying step, and the operation start step of the first adsorption tower are performed. Therefore, the production of carbon dioxide can be smoothly continued even during the replacement of the adsorbent.

In the above production method, it is preferable to maintain the dew point of the refined gas under atmospheric pressure at −20 ° C. or lower. As a result, the condensation and solidification of water and the corrosion of each device by water and carbon dioxide can be suppressed, and the production of carbon dioxide can be further facilitated.

The above manufacturing method preferably has a dehumidifying step of reducing the water content of the raw material gas. As a result, the condensation and solidification of water and the corrosion of each device by water and carbon dioxide can be suppressed, and the production of carbon dioxide can be continued more smoothly.

In the drying step, it is preferable to distribute the purified gas from the lower part to the upper part of the adsorption tower. Since the specific gravity of water vapor is smaller than that of purified gas, the stagnation of water vapor is reduced by circulating in this direction, and the vaporized water can be smoothly discharged from the adsorption tower.

The carbon dioxide producing apparatus according to one aspect of the present disclosure is a carbon dioxide producing apparatus including a plurality of adsorbents containing an adsorbent that adsorbs impurities of a raw material gas containing carbon dioxide, and adsorbs at least one of them. While continuing the production of carbon dioxide using the tower, a part of the purified gas obtained by reducing impurities from the raw material gas is supplied to an adsorption tower different from the adsorption tower, and the adsorption tower is filled with another adsorption tower. It is provided with a supply unit for drying the adsorbent.

In this manufacturing apparatus, the adsorbent is dried by supplying a purified gas obtained by reducing impurities from the raw material gas to the adsorbent tower filled with the adsorbent. Since the production of carbon dioxide can be carried out in parallel while the adsorbent is being dried, it is not necessary to stop the production of carbon dioxide. Therefore, the production loss of high-purity carbon dioxide can be reduced.

The supply unit preferably has a heating unit that heats the purified gas supplied to another adsorption tower. By supplying the heated purified gas to the adsorption tower, the adsorbent can be quickly dried.

The manufacturing apparatus preferably includes a dehumidifying portion that reduces the water content of the raw material gas. As a result, the condensation and solidification of water and the corrosion of each device by water and carbon dioxide can be suppressed, and the production of carbon dioxide can be further facilitated.

It is preferable that the supply unit is connected to the lower side of the adsorption tower rather than the discharge unit that discharges the purified gas used for drying the adsorbent from the adsorption tower. Since the specific gravity of water vapor is smaller than that of purified gas, the stagnation of water vapor can be reduced by connecting the supply and the discharge part in such a positional relationship, and the vaporized water can be smoothly discharged from the adsorption tower. it can.

According to the present disclosure, it is possible to provide a method for producing carbon dioxide capable of reducing the production loss of high-purity carbon dioxide. Further, it is possible to provide a carbon dioxide production apparatus capable of reducing the production loss of high-purity carbon dioxide.

1 (A) and 1 (B) are diagrams for explaining a part of steps in an example of a method for producing carbon dioxide. 2 (A) and 2 (B) are diagrams for explaining a part of the steps in an example of the method for producing carbon dioxide. 3 (A) and 3 (B) are diagrams for explaining a part of the steps in an example of the method for producing carbon dioxide. FIG. 4 is a schematic view showing another example of the carbon dioxide production apparatus.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings in some cases. However, the following embodiments are examples for explaining the present invention, and the present invention is not intended to be limited to the following contents. In the description, the same reference numerals are used for the same elements or elements having the same function, and duplicate description may be omitted in some cases.

The method for producing carbon dioxide according to one embodiment is a method for producing carbon dioxide using a plurality of adsorption towers containing an adsorbent that adsorbs impurities of a raw material gas containing carbon dioxide, and reduces impurities from the raw material gas. It has a purification step of obtaining a refined gas having a higher purity of carbon dioxide than the raw material gas. Then, at a predetermined timing, in parallel with this purification step, there is a drying step of filling at least one adsorption tower with an unused adsorbent and then drying the adsorbent using a part of the refined gas. The number of adsorption towers may be two or three or more. The purification step can be continuously performed even during the drying step by using an adsorption tower different from the adsorption tower on which the drying step is performed. Therefore, carbon dioxide satisfying the product standard can be continuously produced by using the other part of the refined gas even during the drying step. The "unused adsorbent" in the present disclosure means an adsorbent that has not yet been used in the purification process.

The raw material gas containing carbon dioxide is not particularly limited, and examples thereof include combustion gas such as a boiler. The raw material gas may contain impurities in addition to carbon dioxide. Examples of impurities include water, oxygen, nitrogen, sulfur oxides, nitrogen oxides, carbon monoxide, hydrogen sulfide, hydrocarbons and the like. The concentration of carbon dioxide in the raw material gas may be, for example, 95% by volume or more, or 98% by volume or more.

Examples of the adsorbent include commercially available activated carbon and zeolite. In terms of cost, the adsorbent preferably contains activated carbon. The purification step and the drying step are performed in parallel. In the drying step, the adsorbent is dried using the purified gas obtained in the purification step. For drying the adsorbent, a purified gas having reduced impurities is used in an adsorbent tower different from the adsorbent tower filled with the adsorbent to be dried. The refined gas is a gas having a lower concentration of impurities than the raw material gas, and may be carbon dioxide produced in the present embodiment.

The purified gas for drying the adsorbent is preferably supplied from the lower part of the adsorption tower in which the adsorbent is housed. The dry gas containing water desorbed from the adsorbent is preferably discharged from the upper part of the adsorption tower. As a result, the purified gas flows from the lower part to the upper part of the adsorption tower. With such a distribution direction, the vaporized water is smoothly discharged to the outside of the adsorption tower.

The temperature of the purified gas used for drying is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, from the viewpoint of quickly drying the adsorbent. From the viewpoint of preventing ignition of activated carbon and energy efficiency, the temperature of the refined gas used for drying is preferably 200 ° C. or lower, more preferably 160 ° C. or lower, and further preferably 140 ° C. or lower.

The pressure of the purified gas used for drying may be, for example, atmospheric pressure to 1 MPa. The space velocity of the purified gas in the drying step may be 10 to ^{50 h-1.} The time of the drying step may be, for example, 24-48 hours. The determination of the end of the drying step can be made based on, for example, the temperature or dew point of the drying gas derived from the adsorption tower in which the adsorbent is dried. As a result, in the refining step after the drying step, the water content mixed in the carbon dioxide is kept low, and the condensation of the water content and the corrosion of the equipment due to the water and carbon dioxide gas can be sufficiently suppressed. The drying step is terminated when the temperature of the drying gas reaches, for example, 100 ° C. or higher, preferably 110 ° C. or higher, more preferably 120 ° C. or higher.

The adsorption tower after the drying of the adsorbent may be subsequently subjected to a purification step of reducing impurities contained in the raw material gas to obtain a refined gas. The purification step may be carried out using a plurality of adsorption towers. The dew point of the purified gas under atmospheric pressure is preferably maintained at, for example, −20 ° C. or lower, preferably −30 ° C. or lower, and more preferably −40 ° C. or lower. As a result, the amount of water mixed in carbon dioxide is kept low, and the condensation of water and the corrosion of equipment due to water and carbon dioxide can be sufficiently suppressed.

The refined gas obtained in the purification step can be carbon dioxide produced in the present embodiment. The purity of carbon dioxide produced in the present embodiment may be, for example, 99.5% by volume or more, and may be 99.9% by volume or more. However, the purity is not limited, and it is sufficient that the purity of carbon dioxide is higher than that of the raw material gas. Therefore, it may contain impurities. In addition, "volume%" in this disclosure is a volume ratio in a standard state (0 ° C., 1 atm).

A liquefaction step of liquefying carbon dioxide obtained in the purification step may be performed. That is, in the production method of the present embodiment, gaseous carbon dioxide may be produced, or liquid carbon dioxide may be produced. By sufficiently lowering the dew point of the purified gas, solidification of water can be sufficiently suppressed even if the liquefaction step is performed.

For example, when the unused adsorbent contained in the adsorption tower is dried using an inert gas other than carbon dioxide such as nitrogen gas or argon gas, the inside of the adsorption tower is replaced with gas after the unused adsorbent is dried. There is a need. On the other hand, in the production method of the present embodiment, purified gas is used for drying the unused adsorbent in the drying step. Therefore, the consumption of the inert gas can be reduced.

The carbon dioxide production apparatus according to one embodiment includes a plurality of adsorption towers containing an adsorbent that adsorbs impurities of a raw material gas containing carbon dioxide, and continues to produce carbon dioxide using at least one adsorption tower. At the same time, a supply unit that supplies a purified gas obtained by reducing impurities from the raw material gas to an adsorption tower different from the adsorption tower to dry the adsorbent filled in the other adsorption tower, and an adsorbent. It is provided with a discharge unit that discharges the purified gas (dry gas) used for drying the gas from the adsorption tower. The above-mentioned method for producing carbon dioxide may be carried out using such a production apparatus. The above description of the production method can also be applied to the carbon dioxide production apparatus of the present embodiment.

The supply unit may supply a part of carbon dioxide derived from the adsorption tower as a purified gas to the other adsorption tower. The supply unit includes, for example, a pipe for circulating the refined gas and a heating unit for heating the refined gas. By providing the heating portion, the unused adsorbent can be dried more quickly. The heating unit may be, for example, a heat exchanger that uses steam or hot oil as a heat source. The discharge unit includes, for example, a pipe for circulating the dry gas obtained by drying the adsorbent. It is preferable that the supply unit is connected to the lower part of the adsorption tower and the discharge unit is connected to the upper part of the adsorption tower. As a result, the adsorbent is dried by the purified gas (dry gas) rising in the adsorption tower, and the water content of the adsorbent can be smoothly reduced.

The carbon dioxide production apparatus may be provided with a dehumidifying portion on the upstream side of the plurality of adsorption towers. The dehumidifying portion has a function of reducing the water content contained in the raw material gas. By providing the dehumidifying portion, it is possible to suppress the condensation and solidification of water and the corrosion of each device by water and carbon dioxide gas, and further facilitate the production of carbon dioxide.

The carbon dioxide producing apparatus may include a post-treatment unit for liquefying or solidifying carbon dioxide on the downstream side of the adsorption tower. The post-treatment unit has a function of adjusting the temperature and pressure of carbon dioxide, and includes, for example, a compressor and a cooler.

As an example of the carbon dioxide production method and the production apparatus according to the present embodiment, an example including two adsorption towers, a first adsorption tower and a second adsorption tower, will be described below.

1 (A), 1 (B), 2 (A), 2 (B), 3 (A) and 3 (B) describe a part of the steps of the method for producing carbon dioxide. It is a figure for. In this example, a carbon dioxide production apparatus having a first adsorption tower 11 and a second adsorption tower 12 connected so that the raw material gas flows sequentially as a plurality of adsorption towers 10 is used.

In FIG. 1 (A), the raw material gas sequentially flows through the first adsorption tower 11 and the second adsorption tower 12, and the purified gas is obtained (dotted flow in FIG. 1 (A)). Adsorbents 21 and 22 are housed in the first adsorption tower 11 and the second adsorption tower 12, respectively. Impurities other than carbon dioxide contained in the raw material gas are adsorbed on the adsorbents 21 and 22. Purified gas is led out from a pipe connected to the bottom 12b of the second adsorption tower 12. The purification step is performed in this way. This refined gas may be used as it is as carbon dioxide gas, may be cooled by a cooling unit to be liquid carbon dioxide, and then may be used as dry ice. The obtained carbon dioxide may be introduced into, for example, a tank or the like and stored.

In FIG. 1B, the introduction of the raw material gas into the first adsorption tower 11 is stopped, and the raw material gas is introduced into the second adsorption tower 12. While continuing the introduction of the raw material gas into the second adsorption tower 12 and the derivation of the purified gas (carbon dioxide) from the second adsorption tower 12 (broken flow in FIG. 1B), the gas is housed in the first adsorption tower 11. Take out the used adsorbent that had been used (stopping process). After taking out, the unused adsorbent is housed in the first adsorption tower 11. Such exchange of activated carbon may be carried out periodically, or may be carried out when the impurity concentration of the purified gas derived from the first adsorption tower 11 increases.

In FIG. 2A, a part of the purified gas (carbon dioxide) derived from the bottom portion 12b of the second adsorption tower 12 is introduced into the heating portion 30 and heated. The heat source may be steam or hot oil as shown in the figure. The purified gas heated to a predetermined temperature range by the heating unit 30 flows through the pipe 31 and is supplied into the first adsorption tower 11 from the bottom 11b of the first adsorption tower 11. Here, the heating unit 30 and the pipe 31 form a purification gas supply unit.

The purified gas supplied from the supply unit to the first adsorption tower 11 comes into contact with the unused adsorbent while rising in the first adsorption tower 11 to reduce the water content of the unused adsorbent. The purified gas (dry gas) containing water circulates through the pipe 41 (discharge part) connected to the top 11a of the first adsorption tower 11, and is discharged into the atmosphere, for example (dotted line in FIG. 2 (A)). flow). During this drying step, the purified gas derived from the bottom 12b of the second adsorption tower 12 can be continuously produced as carbon dioxide (broken line flow in FIG. 2A).

When the drying of the unused adsorbent is completed, the production of the purified gas is started in the first adsorption tower 11 (operation start step). The end of drying may be determined, for example, by the temperature or dew point of the drying gas derived from the top 11a of the first adsorption tower 11. For example, when the temperature of the dry gas reaches 100 ° C. or lower, preferably 110 ° C. or higher, more preferably 120 ° C. or higher, the supply of the heated purified gas from the bottom 11b of the first adsorption tower 11 is stopped. Then, the purified gas derived from the bottom portion 12b of the second adsorption tower 12 is introduced from the top portion 11a of the first adsorption tower 11 (FIG. 2B). Adsorption of impurities by the unused adsorbent 21 housed in the first adsorption tower 11 is started. The purified gas obtained from the bottom portion 11b of the first adsorption tower 11 can be obtained as carbon dioxide.

FIG. 2B shows a purification step after the operation start step of the first adsorption tower 11. In this purification step, the raw material gas flows through the second adsorption tower 12 and the first adsorption tower 11 in this order, and the refined gas is obtained (dotted line in FIG. 2B). The timing of starting the operation start step of the first adsorption tower 11 after the drying step of the first adsorption tower 11 is not particularly limited, and the first adsorption tower 11 may be paused for a while after the drying step. When the purification step is performed according to the flow shown in FIG. 2B, the adsorption capacity of the adsorbent 22 of the second adsorption tower 12 on the upstream side gradually decreases. For example, when the impurity concentration of the purified gas derived from the second adsorption tower 12 increases, the adsorbent 22 of the second adsorption tower 12 is replaced by the following procedure.

As shown in FIG. 3A, the introduction of the raw material gas into the second adsorption tower 12 is stopped, and the raw material gas is introduced into the first adsorption tower 11. While continuing the introduction of the raw material gas into the first adsorption tower 11 and the derivation of the purified gas from the first adsorption tower 11 (production of carbon dioxide) (broken flow in FIG. 3A), the second adsorption tower 12 Take out the used adsorbent contained in (stopping process). After taking out, the unused adsorbent is housed in the second adsorption tower 12.

As shown in FIG. 3B, after the unused adsorbent is housed in the second adsorption tower 12, a part of the purified gas (carbon dioxide) derived from the bottom 11b of the first adsorption tower 11 is heated by the heating unit 30. Introduce to and heat. The purified gas heated to a predetermined temperature or higher by the heating unit 30 flows through the pipe 32 and is supplied into the second adsorption tower 12 from the bottom 12b of the second adsorption tower 12. Here, the heating unit 30 and the pipe 32 form a purification gas supply unit.

The purified gas supplied from the supply unit to the second adsorption tower 12 comes into contact with the unused adsorbent while rising in the second adsorption tower 12, and reduces the water content of the unused adsorbent. The purified gas (dry gas) containing water circulates through the pipe 42 (discharge part) connected to the top 12a of the second adsorption tower 12, and is discharged into the atmosphere, for example (dotted line in FIG. 3B). ). During this drying step, the purified gas derived from the bottom portion 11b of the first adsorption tower 11 can be continuously produced as carbon dioxide (broken line flow in FIG. 3B).

When the drying of the unused adsorbent contained in the second adsorption tower 12 is completed, the production of the purified gas is started in the second adsorption tower 12 (operation start step). The end of drying may be determined, for example, by the temperature or dew point of the drying gas derived from the top 12a of the second adsorption tower 12. When the drying is completed, the supply of the heated purified gas from the bottom 12b of the second adsorption tower 12 is stopped. Then, as shown in FIG. 1A, the purified gas derived from the bottom portion 11b of the first adsorption tower 11 is introduced from the top portion 12a of the second adsorption tower 12. In this way, the adsorption of impurities by the unused adsorbent 22 housed in the second adsorption tower 12 is started. The purified gas obtained from the bottom 12b of the second adsorption tower 12 can be used as carbon dioxide. By repeating the steps of FIGS. 1 to 3 in this way, the loss of carbon dioxide at the time of exchanging the adsorbent can be reduced, and the amount of high-purity carbon dioxide produced can be sufficiently increased.

FIG. 4 is a schematic view showing another example of the carbon dioxide production apparatus. The manufacturing apparatus of FIG. 4 is an apparatus for producing carbon dioxide from exhaust gas such as a boiler. This manufacturing apparatus includes a desulfurization tower 50, an absorption tower 60, a regeneration tower 80, a compressor 90, a dehumidifying unit 95, and an adsorption tower 10. The exhaust gas is introduced into the desulfurization tower 50. The desulfurization tower 50 removes, for example, sulfur oxides contained in the exhaust gas. For example, an alkaline aqueous solution is supplied to the desulfurization tower 50. In the desulfurization tower 50, the exhaust gas and the alkaline aqueous solution come into gas-liquid contact, and the sulfur oxide is absorbed by the alkaline aqueous solution. Examples of the alkaline aqueous solution include calcium carbonate aqueous solution, sodium hydroxide aqueous solution, magnesium hydroxide aqueous solution, ammonia water and the like.

The exhaust gas that has passed through the desulfurization tower 50 is supplied to the absorption tower 60. In the absorption tower 60 and the regeneration tower 80, carbon dioxide is recovered from the exhaust gas by a chemical absorption method. The absorption tower 60 brings the exhaust gas generated by the boiler or the like into contact with the absorption liquid that absorbs carbon dioxide, and causes the absorption liquid to absorb the carbon dioxide contained in the exhaust gas.

The absorption liquid is supplied to the absorption tower 60 from the flow path 84 connected to the upper portion thereof. The absorbing liquid is a liquid that absorbs carbon dioxide, for example, an aqueous amine solution. Examples of the amine aqueous solution include aqueous solutions such as MEA (monoethanolamine), EAE (ethylaminoethanol), IPAE (isopropaaminoethanol), and TMDAH (tetramethyldiaminohexane).

In the absorption tower 60, the raw material gas rises as the absorption liquid falls. As a result, the absorption liquid and the raw material gas come into countercurrent contact, and the carbon dioxide contained in the raw material gas is absorbed by the absorption liquid. The amount of carbon dioxide absorbed by the absorption liquid depends on the temperature. Therefore, the amount of carbon dioxide absorbed by the absorption liquid can be adjusted by controlling the temperature inside the absorption tower 60.

In the absorption tower 60, the absorption liquid descends while in gas-liquid contact with the exhaust gas to absorb carbon dioxide contained in the exhaust gas (absorption step). The gas (off gas) from which carbon dioxide has been reduced or removed is discharged from the top of the absorption tower 60 and introduced into the scrubber 65. Water is supplied to the scrubber 65 by a flow path (not shown). In the scrubber 65, the trace components contained in the gas are removed by bringing the gas into contact with water. The gas washed in the scrubber 65 may be released into the atmosphere or may be used for various purposes depending on the components contained.

The temperature inside the absorption tower 60 can be set according to, for example, the type of the absorbing liquid, and is, for example, 30 to 40 ° C. The pressure in the absorption tower 60 is, for example, 0 to 1.0 MPa.

The absorption liquid (rich liquid) that has absorbed carbon dioxide in the absorption tower 60 is stored in the bottom of the absorption tower 60 and discharged from the absorption tower 60 at 30 to 40 ° C. by the flow path 62 connected to the bottom of the tower. To the tower. The absorbing liquid discharged from the absorption tower 60 is introduced into the heat exchanger 70 via a pump. Here, heat is exchanged with the absorbing liquid (lean liquid) discharged from the regeneration tower 80 through the flow path 83, and the heat is heated to, for example, 80 to 90 ° C. The absorbing liquid heated by the heat exchanger 70 flows through the flow path 64 and is introduced into the regeneration tower 80. The flow path 64 is connected to the upper part of the regeneration tower 80.

The absorption liquid (rich liquid) that has absorbed carbon dioxide introduced into the regeneration tower 80 flows down in the regeneration tower 80. At that time, carbon dioxide is separated from the absorbing liquid (rich liquid), and the absorbing liquid is regenerated. The absorbing liquid that has flowed down in the regeneration tower 80 stays on the bottom of the regeneration tower 80 or on a tray (not shown) provided near the bottom of the tower. A reboiler 81 for heating the absorption liquid staying at the bottom of the regeneration tower 80 or near the bottom of the regeneration tower 80 is provided outside the regeneration tower 80. The absorbing liquid staying on the tray is introduced into the reboiler 81, exchanges heat with a heat medium (for example, water vapor), and is heated to, for example, 80 to 130 ° C. The absorption liquid heated by the reboiler 81 returns to the inside of the regeneration tower 80.

A flow path 83 for discharging an absorption liquid (lean liquid) having reduced carbon dioxide from the regeneration tower 80 is connected to the bottom of the regeneration tower 80. The absorption liquid (lean liquid) flows through the flow path 83 and is introduced into the heat exchanger 70, and is cooled by heat exchange with the absorption liquid (rich liquid) from the absorption tower 60. After that, the absorbing liquid (lean liquid) cooled by the heat exchanger 70 flows through the flow path 84 and is introduced into the cooler 82, and is cooled to, for example, 30 to 40 ° C. After that, the absorption liquid (lean liquid) is supplied to the upper part of the absorption tower 60. In this way, the absorbing liquid is used while circulating between the absorption tower 60 and the regeneration tower 80.

In the regeneration tower 80, the gas containing carbon dioxide and impurities separated from the absorption liquid rises in the regeneration tower 80 and is derived from the top of the regeneration tower 80 as a raw material gas for the adsorption tower 10. The raw material gas is taken out from the top of the regeneration tower 80 at a temperature of, for example, 85 to 95 ° C., introduced into a heat exchanger, and cooled to 30 to 50 ° C. by heat exchange with water, for example. The condensate produced by cooling is used as a reflux in the regeneration tower 80.

The raw material gas cooled by the heat exchanger is introduced into the compressor 90 and boosted to, for example, 0.8 to 1 MPa. The raw material gas pressurized by the compressor 90 is introduced into the dehumidifying section 95. The dehumidifying section 95 has a dehumidifying material such as activated alumina or zeolite. By introducing the raw material gas into the dehumidifying section 95 in the above pressure range, the water content in the raw material gas can be efficiently reduced. Moisture is removed from the raw material gas in the dehumidifying section 95, and the dew point is adjusted to, for example, −40 ° C. or lower. As a result, it is possible to suppress the condensation and solidification of water on the downstream side. In addition, corrosion due to water and carbon dioxide can be sufficiently suppressed.

The raw material gas dehumidified in the dehumidifying section 95 is introduced into the adsorption tower 10 in which the adsorbent is housed. The adsorption tower 10 may have a configuration including two adsorption towers as shown in FIGS. 1 to 3, or may have a different configuration. With the carbon dioxide production apparatus as shown in FIG. 4, the production amount of high-purity carbon dioxide can be smoothly increased from the exhaust gas containing carbon dioxide.

Although some embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, a catalyst tower containing a reduction catalyst may be provided on the upstream side of the adsorption tower 10. In the case of the catalyst tower, when the raw material gas comes into contact with the reduction catalyst in a hydrogen atmosphere, impurities contained in the raw material gas can be reduced and the purity of carbon dioxide can be further improved. As the reduction catalyst used in the catalyst tower, a known deoxidizing catalyst can be used. For example, a catalyst in which a noble metal is supported on a carrier can be mentioned. Examples of carriers include aluminum oxide and magnesium oxide. Examples of precious metals include platinum, palladium, rhodium, ruthenium and alloys thereof. As the carrier and the noble metal, the above-mentioned one type may be used alone, or two or more types may be combined. Since carbon dioxide produced by the above-mentioned production apparatus or production method has a reduced odor, it can be suitably used for, for example, beverage or food applications.

The contents of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

(Example 1)
The used activated carbon was replaced in the carbon dioxide production apparatus in the operating state shown in FIG. 1 (A). The exchange was performed as shown in FIG. 1 (B). That is, the introduction of the raw material gas into the first adsorption tower 11 was stopped, and the raw material gas was introduced into the second adsorption tower 12. While continuing the production of carbon dioxide in the second adsorption tower 12, the used activated carbon contained in the first adsorption tower 11 was taken out. After taking out, unused activated carbon was housed in the first adsorption tower 11.

Next, the unused activated carbon was dried as shown in FIG. 2 (A). That is, a part of carbon dioxide (about 20% by volume of the total amount) derived from the bottom 12b of the second adsorption tower 12 was introduced into the heating unit 30 as a purified gas and heated. Steam was used as the heat source. The purified gas heated to 120 to 130 ° C. by the heating unit 30 was supplied into the first adsorption tower 11 from the bottom 11b of the first adsorption tower 11. From the time when the step (flow) shown in FIG. 2 (A) was started, the temperatures and dew points of the lower and upper parts of the first adsorption tower 11 were monitored.

Immediately after the start of the process, there was no significant change in temperature due to the latent heat of vaporization of the adsorbent. However, as the drying of the adsorbent progressed, the temperature of the lower part of the first adsorption tower 11 first rose, and the temperature of the upper part rose accordingly. When the temperature of the upper part rose to around 120 ° C. and the dew point reached −40 ° C., it was determined that the drying of the adsorbent was completed. The time required from the start of the step (flow) shown in FIG. 2 (A) to the completion of drying of the adsorbent was about 24 hours. Further, while the adsorbent was being dried, the purity of carbon dioxide was 99.9% by volume or more, and the production of carbon dioxide satisfying the product standard of the dew point could be continued.

(Comparative Example 1)
Production of carbon dioxide when the used activated carbon is replaced in the same manner as in Example 1 and then the unused activated carbon is dried by the flow of FIG. 2 (B) instead of the flow of FIG. 2 (A). The loss was simulated. That is, it was premised that all of the refined gas obtained in the second adsorption tower 12 was introduced into the first adsorption tower 11 and the unused activated carbon was dried using the refined gas. After the start of drying, the dew point of carbon dioxide derived from the first adsorption tower 11 is high and the product standard cannot be satisfied, so that the product cannot be produced and must be released to the atmosphere. It takes several days to a week for the dew point to meet the product standard. During that time, carbon dioxide cannot be produced. In addition, the amount of carbon dioxide emitted is increased about 15 times as compared with Example 1, and the production loss is increased.

According to the present disclosure, it is possible to provide a method for producing carbon dioxide capable of reducing the production loss of high-purity carbon dioxide. Further, it is possible to provide a carbon dioxide production apparatus capable of reducing the production loss of high-purity carbon dioxide.

10 ... Adsorption tower, 11 ... First adsorption tower, 11a, 12a ... Top, 11b, 12b ... Bottom, 12 ... Second adsorption tower, 21,22 ... Adsorbent, 30 ... Heating part, 31, 32, 41, 42 ... piping, 50 ... desulfurization tower, 60 ... absorption tower, 62, 64, 83, 84 ... flow path, 65 ... cleaning tower, 70 ... heat exchanger, 80 ... regeneration tower, 81 ... reboiler, 82 ... cooler, 90 ... Compressor, 95 ... Dehumidifying part.

Claims (6)

A method for producing carbon dioxide, which comprises a plurality of adsorption towers in which an adsorbent that adsorbs impurities of a raw material gas containing carbon dioxide is accommodated and connected so that the raw material gas is sequentially distributed.
The plurality of adsorption towers have a first adsorption tower and a second adsorption tower.
While continuing the production of carbon dioxide in the second adsorption tower, a stop step of taking out the used adsorbent of the first adsorption tower in which the introduction of the raw material gas is stopped, and
Unused adsorbent is filled the first adsorption tower, and Drying step you drying part test sheet above unused adsorbent purified gas derived from the second adsorption tower,
After drying the unused adsorbent, have a, and operation start obtaining carbon dioxide from the first adsorption tower,
Wherein in the operation start step, determining the end of the drying unused adsorbent at a temperature or dew point of the drying gas derived from the first adsorption tower, the production method of carbon dioxide. The method for producing carbon dioxide according to claim 1, wherein in the drying step, a part of the purified gas is heated and then the purified gas is supplied to the adsorption tower filled with the adsorbent. The method for producing carbon dioxide according to claim 1 or 2, wherein the dew point of the refined gas under atmospheric pressure is maintained at −20 ° C. or lower. The method for producing carbon dioxide according to any one of claims 1 to 3 , further comprising a dehumidifying step of reducing the water content of the raw material gas. The method for producing carbon dioxide according to any one of claims 1 to 4 , wherein in the drying step, the purified gas is circulated from the lower part to the upper part of the first adsorption tower. The method for producing carbon dioxide according to any one of claims 1 to 5, wherein carbon dioxide having a purity of 99.9% by volume or more is continuously produced in the drying step.

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