WO2011007752A1 - Method for removing impurities from carbon dioxide gas - Google Patents

Abstract

Provided is a method for removing impurities from carbon dioxide gas, which comprises: a step in which crude carbon dioxide gas containing high-boiling-point impurities and low-boiling-point impurities is fed to a liquid carbon dioxide purification column, a predetermined amount of the fed crude carbon dioxide gas is introduced to the column top, and the liquid carbon dioxide containing the high-boiling-point impurities is discharged from the liquid carbon dioxide purification column base to outside the system, thereby removing the high-boiling-point impurities contained in the crude carbon dioxide gas; and a step in which the carbon dioxide gas discharged from the column top is split into a first and a second carbon dioxide gas current, the first carbon dioxide gas current is introduced to a liquefier at the purification column top in order to fully condense the current to liquid carbon dioxide, and the liquid carbon dioxide is introduced to a vapor-liquid separator at the purification column top while the second carbon dioxide gas current is mixed therewith in order to separate the low-boiling-point impurities contained in the liquid carbon dioxide by reflashing in the vapor-liquid separator at the purification column top.

Description

Method for removing impurities in carbon dioxide

The present invention relates to a method for removing impurities in carbon dioxide gas.
This application claims priority based on Japanese Patent Application No. 2009-165407 filed in Japan on July 14, 2009, the contents of which are incorporated herein by reference.

The crude carbon dioxide gas produced as a by-product in the purification process of natural gas and petroleum refinery gas is further processed into a carbon dioxide product for industrial, food and medical use through a purification process for removing impurities. The quality of the product carbon dioxide purified in this way is regulated by JIS K 1106 for industrial use, by the Food Additives Official Code of the Food Sanitation Act, and by the Pharmaceutical Affairs Law for medical use.

Here, as impurities contained in the crude carbon dioxide gas, for example, methane (boiling point−161.5 ° C.), ethane (boiling point−89.0 ° C.), propane (boiling point−42.1 ° C.), carbon monoxide (boiling point) -192 ° C), hydrogen (boiling point -252.5 ° C), oxygen (boiling point -183.0 ° C), nitrogen (boiling point -195.8 ° C), hydrogen sulfide (boiling point -60.7 ° C), etc. There are low-boiling substances that vaporize at extremely low temperatures (hereinafter referred to as low-boiling impurities). In recent years, high-boiling substances mainly composed of benzene (boiling point 80 ° C.), toluene (boiling point 111 ° C.), para-xylene (boiling point 138 ° C.), etc., in consideration of environmental problems when carbon dioxide is injected underground. (Hereinafter referred to as “high-boiling-point impurities”) also needs to be removed as impurities. In addition, the boiling point of the above-mentioned substance is a boiling point under atmospheric pressure.

In normal carbon dioxide purification, after removing water, crude carbon dioxide gas is supplied to the liquid carbonic acid rectification tower, low-boiling impurities are driven up to the top of the liquid carbonic acid rectification tower, and discharged out of the system. A high-purity liquid carbonic acid containing no low-boiling-point impurities is obtained at the bottom of the rectifying column, and this is used as a product. In recent years, in the separation and recovery of carbon dioxide gas, the conventional hot potassium carbonate absorption method has been replaced with an amine absorption method using amines having excellent thermal economy.

When amines are used as an absorbing solution compared to hot potassium carbonate, the amine is an organic substance, so that the dissolution of hydrocarbons increases, and low-boiling impurities such as alkanes such as methane, ethane, and propane, alkenes, and alkynes. In addition, even high-boiling hydrocarbons such as benzene, toluene, and xylene are included in the crude carbon dioxide gas obtained from the decarboxylation apparatus. In the conventional carbon dioxide purification method, low boiling point impurities are removed, but the purified liquid carbonic acid taken out from the bottom of the liquid carbonic acid rectification tower contains high boiling point impurities almost as it is. .

In relation to such a situation, for example, in Patent Document 1 and Patent Document 2 below, the amount of carbon dioxide gas that is driven up to the top of a liquid carbonic acid rectification column and discarded outside the system is reduced. In order to improve, a method of removing low boiling point impurities in advance from a raw raw carbon dioxide gas using a desulfurization catalyst, an oxidation catalyst or the like before liquefying the carbon dioxide gas is shown.

Also, a method for removing high boiling impurities by, for example, an adsorption operation using activated carbon or the like is known.

Japanese Patent Laid-Open No. 10-130009 Japanese Patent Laid-Open No. 11-209117

However, in the conventional purification method, a temperature of 150 ° C. to 200 ° C. is necessary for the conversion and removal of low boiling point impurities by the catalyst, and 200 ° There was a problem that a temperature of about 0 ° C. was necessary and it was not economical.

In recent years, high-boiling hydrocarbons such as benzene, toluene, xylene and the like contained in the crude carbon dioxide gas obtained from the decarbonation apparatus have all been subjected to liquid carbonation rectification in the conventional method. There was a problem that the product liquid carbon dioxide present at the bottom of the tower was mixed and not purified. In addition, even if these high-boiling impurities are adsorbed on activated carbon before the high-boiling impurities are liquefied, there is a problem that a great deal of heat is required to regenerate the activated carbon.

In addition, benzene and para-xylene are high-melting substances having melting points of 5.5 ° C. and 13 ° C., respectively, so that these substances are not removed and supplied to the liquid carbonic acid rectification column as raw carbon dioxide gas. In such a case, the solidification may occur in the liquid carbonic acid rectification column usually operated at −14 to −18 ° C., and the apparatus may be blocked.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to economically remove both low-boiling point impurities and high-boiling point impurities in the crude carbon dioxide gas. An object of the present invention is to provide a method for removing impurities in carbon dioxide gas, which can obtain product carbon dioxide gas in a recovery rate.

In order to solve the above-described problems, according to a certain aspect of the present invention, a low-boiling point impurity, which is an impurity having a higher boiling point than carbon dioxide gas and an impurity having a lower boiling point than carbon dioxide gas, contained in the crude carbon dioxide gas. A method for removing boiling point impurities from the crude carbon dioxide gas, the method comprising: removing the high boiling point impurities from the crude carbon dioxide gas; and removing the low boiling point impurities from the crude carbon dioxide gas. . The step of removing the high-boiling-point impurities includes the step of supplying the crude carbon dioxide gas containing the high-boiling-point impurities and the low-boiling-point impurities to a liquid carbonic acid rectification column; A step of introducing a predetermined amount of the supply amount of the crude carbon dioxide gas to the top of the column, and a step of discharging the liquid carbon dioxide containing the high-boiling impurities from the bottom of the liquid carbonic acid rectification column to the outside of the system. The step of removing the low-boiling-point impurities comprises converting the carbon dioxide discharged from the top of the column into a first carbon dioxide gas stream having a relatively high flow rate and a second carbon dioxide gas stream having a relatively low flow rate. A step of diverting, a step of introducing the first carbon dioxide gas stream to a rectifying column top liquefier to completely condense into liquid carbonic acid, and introducing the liquid carbonic acid to a rectifying column top gas-liquid separator; And mixing the low-boiling-point impurities in the liquid carbon dioxide with the rectifying column top gas-liquid separator by reflashing.

The step of removing the high-boiling-point impurities further includes supplying the crude carbon dioxide gas containing the high-boiling-point impurities and the low-boiling-point impurities to any one of a plurality of rectification column pre-liquefiers. A step of cooling to a temperature lower than the temperature at the top of the column, solidifying the high-boiling impurities having a high melting point higher than the temperature at the top of the liquid carbonic acid fractionation column contained in the crude carbon dioxide gas, Supplying the crude carbon dioxide gas from which high melting point impurities having a melting point have been partially removed to the liquid carbonic acid distillation column, and supplying the crude carbon dioxide gas when the high boiling point impurities having a high melting point are blocked. The other rectification column pre-liquefaction device is operated instead of the rectification column pre-liquefaction device, and the carbon dioxide gas discharged from the rectification column top gas-liquid separator and heated to normal temperature is Supplied to the liquefier before the rectification column where high boiling point impurities are blocked, The high boiling-based impurities melting point may be removed by evaporation, sublimation.

The carbon dioxide gas containing the low-boiling-point impurities that are driven up to the top of the liquid carbonic acid rectification column is 95% or more and 97% or less of the supply amount of the crude carbonic acid gas, excluding the reflux that returns to the liquid carbonic acid rectification column. It is preferable.

The first carbon dioxide gas flow is 90 to 99% of the flow rate of the carbon dioxide gas discharged from the tower top, and the second carbon dioxide gas flow is 1 of the flow rate of the carbon dioxide gas discharged from the tower top. It is preferably ˜10%.

In order to solve the above problems, according to another aspect of the present invention, high-boiling impurities that are impurities having a higher boiling point than carbon dioxide gas and impurities having a lower boiling point than carbon dioxide gas are included in the crude carbon dioxide gas. Is a device for removing low boiling point impurities from the crude carbon dioxide gas, wherein the crude carbon dioxide gas is supplied, the low boiling point impurities contained in the crude carbon dioxide gas are led to the top of the tower, and the high boiling point impurities are A liquid carbonate rectification tower for concentrating the system impurities to the bottom of the tower, and a refinement of liquid carbonate by partially condensing a part of the carbon dioxide gas containing the low-boiling-point impurities discharged from the top of the liquid carbonate rectification tower. A rectifying tower top liquefier, liquid carbonate liquefied by the rectifying tower top liquefier, and the remainder of the carbon dioxide gas containing the low-boiling-point impurities discharged from the liquid carbonate rectifying tower top. The low boiling point impurities by reflash Removal of impurities in carbon dioxide gas comprising a rectifying column top gas-liquid separator to be separated and removed, and a purge line for discharging the concentrated high boiling point impurities out of the system from the bottom of the liquid carbonic acid rectifying column An apparatus is provided.

The crude carbon dioxide gas supplied to the liquid carbonic acid rectification tower is cooled, and the high-boiling impurities having a high melting point higher than the tower top temperature in the liquid carbonic acid rectification tower contained in the crude carbonic acid gas. The crude carbon dioxide gas supplied to the rectification column pre-liquefier is further provided with a plurality of rectification column pre-liquefaction devices that solidify and partially remove the high-boiling-point high-boiling impurities from the crude carbon dioxide gas, At the time when the rectifying column pre-liquefier to which the crude carbon dioxide gas is supplied is blocked by the high-melting-point high-boiling-point impurities, the rectifying column pre-liquefaction device is supplied to the other rectifying column pre-liquefier, The high-melting-point high-boiling impurities deposited in the vessel may be evaporated and sublimated by carbon dioxide gas discharged from the rectifying column top gas-liquid separator and heated to room temperature.

The carbon dioxide gas supplied to the rectification column top liquefier is 90 to 99% of the flow rate of the carbon dioxide gas discharged from the column top, and the carbon dioxide gas supplied to the rectification column top gas-liquid separator is The flow rate of carbon dioxide discharged from the top of the column is preferably 1 to 10%.

The low-boiling impurities are C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes, and the high-melting high-boiling impurities may be C6 or higher aromatic hydrocarbons.

As described above, according to the present invention, it is possible to economically remove both low-boiling point impurities and high-boiling point impurities in the crude carbon dioxide gas and obtain a product carbon dioxide gas with a high recovery rate.

It is explanatory drawing for demonstrating the removal apparatus of the impurity in the carbon dioxide gas which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the freezing apparatus which concerns on the same embodiment. It is explanatory drawing for demonstrating the removal apparatus of the impurity in the carbon dioxide gas which concerns on the 2nd Embodiment of this invention. It is explanatory drawing for demonstrating the rectification column pre-liquefaction device which concerns on the same embodiment. It is explanatory drawing for demonstrating the removal apparatus of the impurity in the conventional carbon dioxide gas.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

In the following description, the low boiling point impurities are impurities contained in the crude carbon dioxide gas and have a boiling point lower than that of the carbon dioxide gas, and the high boiling point impurities are contained in the crude carbon dioxide gas, It is an impurity having a boiling point higher than that of carbon dioxide. The temperature at which carbon dioxide gas liquefies varies depending on various environments in which impurity removal devices such as pressure applied to the system are installed, so the reference temperature when classifying low-boiling impurities and high-boiling impurities is also Depending on various environments in which the impurity removing device is installed, the temperature varies.

Here, the low boiling point impurities are impurities contained in natural gas or petroleum refinery gas, or impurities generated in the purification process of these gases. For example, methane (boiling point −161.5 ° C.), ethane (Boiling point-89.0 ° C), propane (boiling point-42.1 ° C), butane (boiling point -0.5 ° C), C1-C4 alkanes, C2-C4 alkenes, C2-C4 alkynes, etc. Light hydrocarbons, carbon monoxide (boiling point -192 ° C), hydrogen (boiling point -252.5 ° C), oxygen (boiling point -183.0 ° C), nitrogen (boiling point -195.8 ° C), hydrogen sulfide (boiling point) −60.7 ° C.).

The high-boiling impurities are impurities contained in natural gas or petroleum refinery gas, or impurities generated in the purification process of these gases. For example, benzene (boiling point 80 ° C.), toluene (boiling point 111 ° C.). ), C6 or higher aromatic hydrocarbons such as para-xylene (boiling point 138 ° C.).

Note that the boiling points of the illustrated low boiling point impurities and high boiling point impurities are those under atmospheric pressure, and are higher in the impurity removal apparatus according to each embodiment of the present invention depending on the pressure in the apparatus. Note that the temperature.

<Regarding conventional impurity removal apparatus>
Prior to describing an apparatus for removing impurities in carbon dioxide gas (hereinafter simply referred to as an impurity removing apparatus) according to each embodiment of the present invention, a conventional apparatus for removing impurities in carbon dioxide gas will be described with reference to FIG. Briefly described, the object of the present invention will be clarified.

FIG. 5 is an explanatory diagram for explaining a conventional apparatus for removing impurities in carbon dioxide gas.
For example, as shown in FIG. 5, the conventional impurity removing apparatus 10 includes a liquid carbonate rectification column 11, a rectification column reboiler 13, a liquid carbonate supercooler 15, a rectification column top liquefier 17, A distillation column top gas-liquid separator 19, a column top purge gas heater 21, and a pressure control valve 23 are provided. In addition, the impurity removing apparatus 10 is provided with a refrigeration apparatus 25.

Crude carbon dioxide gas is supplied to the liquid carbonic acid fractionator 11. The liquid carbonic acid rectification column 11 guides low-boiling impurities to the top of the liquid carbonic acid rectification column 11 and discharges them out of the system to perform rectification of the supplied crude carbon dioxide gas. A part of the rectified carbon dioxide gas is liquefied and present as liquid carbonic acid at the bottom of the liquid carbonic acid rectifying column 11. This liquid carbonic acid is high-purity liquid carbonic acid that does not contain low-boiling-point impurities.

The rectifying tower reboiler 13 is provided in the liquid carbonic acid rectifying tower 11 and supplies heat necessary for the rectifying in the liquid carbonic acid rectifying tower 11. Specifically, the rectification tower reboiler 13 uses the sensible heat of the liquid refrigerant (more specifically, the pre-expansion liquid refrigerant) supplied from the refrigeration apparatus 25, and the amount of heat required for the liquid carbonic acid rectification tower 11. Supply.

The liquid carbonic acid supercooler 15 is supplied with liquid carbonic acid extracted from the bottom of the liquid carbonic acid rectification column 11. The liquid carbonic acid supercooler 15 uses the liquid refrigerant supplied from the refrigeration apparatus 25 to bring the liquid carbonic acid into a supercooled state to produce product liquid carbonic acid.

The rectification tower top liquefier 17 liquefies carbon dioxide gas containing low-boiling-point impurities discharged from the top of the liquid carbonate rectification tower 11 using the liquid refrigerant discharged from the rectification tower reboiler 13, Carbonate. The refrigerant that has become gas in the rectification tower top liquefier 17 is guided to the refrigeration apparatus 25. Further, liquid carbon dioxide, which is liquefied carbon dioxide gas, is guided to the rectification tower top gas-liquid separator 19 described later, and gas containing low-boiling point impurities that have not been liquefied is guided to the tower top purge gas heater 21. Is done.

The rectifying tower top gas-liquid separator 19 separates the liquid carbonic acid supplied from the rectifying tower top liquefier 17 into a gas and a liquid. The liquid carbon dioxide from which the gas component has been separated is supplied again to the liquid carbonic acid fractionator 11 as reflux.

The tower top purge gas heater 21 heats the gas containing the low boiling point impurities discharged from the rectification tower top liquefier 17 to a predetermined temperature (for example, room temperature). The heated gas containing the low-boiling-point impurities is diffused into the atmosphere or flared and discharged outside the apparatus.

The pressure control valve 23 is provided on the downstream side of the tower top purge gas heater 21. By controlling the opening and closing of the pressure control valve 23, the pressure of the entire impurity removing device 10 can be adjusted. Thereby, the impurity removal apparatus 10 can adjust the boiling point etc. of a carbon dioxide gas to the temperature suitable for the environment etc. in which the own apparatus was installed.

The refrigeration apparatus 25 is an apparatus that realizes a temperature environment required in the impurity removal apparatus 10 using a predetermined refrigerant.

In the conventional impurity removing apparatus 10 composed of the apparatus group as described above, the low boiling point impurities contained in the crude carbon dioxide gas supplied to the liquid carbonic acid rectification column 11 are driven up to the top of the liquid carbonic acid rectification column 11. While discharging out of the system, high-purity liquid carbonic acid containing no low-boiling-point impurities is purified at the bottom of the liquid carbonic acid rectifying column 11. Further, the gas containing low-boiling-point impurities discharged from the top of the tower is flared or diffused into the atmosphere through processing by devices such as the rectifying tower top liquefier 17 and the tower top purge gas heater 21.

Under circumstances where conventional high-boiling impurities need not be taken into account, the conventional impurity removal apparatus 10 as shown in FIG. 5 is used to efficiently remove low-boiling impurities from the crude carbon dioxide gas. Is possible. However, in the case of handling crude carbon dioxide by-produced by a method in which not only low boiling point impurities but also high boiling point impurities are mixed in the crude carbon dioxide gas as in the amine absorption method used in recent years, The impurity removing apparatus 10 as shown in FIG. 5 is insufficient. That is, in the impurity removing apparatus 10 as shown in FIG. 5, all of the high-boiling impurities are mixed in the product liquid carbonic acid present at the bottom of the liquid carbonic acid distillation column 11, and the product liquid carbonic acid is not purified. It will be used as.

Further, as a method for removing high-boiling impurities, a method using activated carbon is known, but even if such a method is applied to the impurity removal apparatus 10 shown in FIG. However, there is a problem that it is not easy to remove the high-boiling-point impurities, and it is not economical.

Therefore, the present inventors have solved the above-mentioned problems, and simultaneously and economically removed the low boiling point impurities and the high boiling point impurities in the crude carbon dioxide gas, so that the product carbon dioxide gas can be removed at a high recovery rate. As a result of diligent research to realize a method that can be obtained, an apparatus and a method for removing impurities in carbon dioxide gas according to each embodiment of the present invention described below have been conceived.

Hereinafter, an apparatus and a method for removing impurities in carbon dioxide gas according to each embodiment of the present invention will be described in detail with reference to FIGS.

(First embodiment)
<About impurity removal equipment>
Subsequently, the impurity removing apparatus according to the first embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is an explanatory diagram for explaining an impurity removing apparatus 100 according to the present embodiment, and FIG. 2 is an explanatory diagram for explaining a refrigeration apparatus according to the present embodiment.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a very small amount of liquid carbonic acid that exists at the bottom of the liquid carbonic acid rectification column and contains high-boiling-point impurities is contained outside the system. It was conceived that it is possible to remove high boiling point impurities by discharging to a low temperature. Therefore, if most of the carbon dioxide gas supplied to the top of the liquid carbonic acid rectification tower is chased and condensed with the rectification tower top liquefier, a product liquid carbonic acid containing almost no high-boiling-point impurities can be obtained. Is possible. However, at this time, there remains a problem that low-boiling impurities are concentrated at the top of the liquid carbonic acid rectification column. As a result of further studies, the present inventors have come up with an impurity removal apparatus and an impurity removal method according to the first embodiment of the present invention as described below.

For example, as shown in FIG. 1, the impurity removing apparatus 100 according to the present embodiment includes a liquid carbonic acid rectifying column 101, a rectifying column reboiler 103, a rectifying column top liquefier 105, and a rectifying column top gas liquid. The separator 107, the product liquid carbonate supercooler 109, the tower top purge gas heater 111, the pressure control valve 113, the purge line 115, the tower bottom purge liquid carbon dioxide evaporator 117, and the refrigeration apparatus 121 are mainly used. Prepare for.

The liquid carbonic acid rectification column 101 performs rectification of the supplied crude carbon dioxide gas, and guides low-boiling impurities contained in the crude carbon dioxide gas to the top of the column. In addition, a part of the rectified carbon dioxide gas is liquefied and present as liquid carbonic acid at the bottom of the liquid carbonic acid rectifying column 101. In this liquid carbonic acid, concentrated high boiling point impurities are present.

In this liquid carbonic acid distillation column 101, high boiling point impurities are concentrated at the bottom of the column. The amount of heat required for rectification is supplied from the rectification tower reboiler 103. When the pressure at the top of the column is adjusted to an appropriate value, for example, 2.3 MPaG, by the pressure control valve 113, the temperature of each part of the liquid carbonic acid distillation column 101 is determined according to the pressure.

In this liquid carbonic acid rectification column 101, a predetermined amount of the supply amount of the crude carbon dioxide gas supplied to the liquid carbonic acid rectification column 101 is purged as liquid carbonic acid from the bottom of the liquid carbonic acid rectification column 101. The amount of column bottom purge liquid carbonic acid is set to a value such that the concentration of high-boiling impurities such as benzene existing near the column top is 1 ppm or less. For example, when the concentration of high-boiling impurities such as benzene in the crude carbon dioxide is several thousand ppm, such a column bottom purge liquid carbonic acid amount is, for example, 3 mol% or more and 5 mol% or less of the number of feed moles. It is possible to set. By setting such a value as the amount of carbon dioxide purge liquid at the bottom of the column, the concentration of high boiling impurities present near the top of the column can be reduced to 1 ppm or less. When the bottom purge liquid carbonic acid content is less than 3 mol%, it is difficult to make the concentration of high boiling impurities present near the top of the tower 1 ppm or less, which is not preferable. Further, when the amount of carbon dioxide purged at the bottom of the column is more than 5 mol%, the yield of product liquid carbonic acid is deteriorated, which is not preferable. Further, as apparent from the fact that the amount of carbon dioxide purged at the bottom of the column is 3 mol% to 5 mol%, the amount of carbon dioxide gas that is driven up to the top of the liquid carbonic acid rectifying column 101 is the amount of liquid carbon dioxide as reflux. The amount returned to the distillation is subtracted, and is 95 volume% to 97 volume% of the supply amount of the crude carbon dioxide gas supplied to the liquid carbonic acid fractionator 101.

When the carbon dioxide gas containing the low-boiling-point impurities discharged from the top of the liquid carbonic acid rectifying column 101 is guided to the rectifying column top liquefier 105 or the rectifying column top gas-liquid separator 107 described later, Divided into two streams. The two flows are a first carbon dioxide gas flow having a relatively high flow rate and a second carbon dioxide gas flow having a relatively low flow rate.

The first carbon dioxide gas flow accounts for 90 to 99% of the flow rate of the carbon dioxide gas discharged from the top of the liquid carbonic acid distillation column 101, for example. Further, the second carbon dioxide gas flow occupies 1 to 10% of the flow rate of the carbon dioxide gas discharged from the top of the liquid carbonic acid distillation column 101, for example. By setting the flow rate of the second carbon dioxide gas flow to 1 to 10%, the impurity removing apparatus 100 can efficiently remove low-boiling impurities contained in the crude carbon dioxide gas, and the impurity removing apparatus 100. The internal pressure can be kept at a substantially constant value. When the flow rate of the second carbon dioxide gas flow is less than 1%, it is not preferable because it is difficult to sufficiently remove the low boiling point impurities in the crude carbon dioxide gas. Further, if the flow rate of the second carbon dioxide gas flow exceeds 10%, it is not economical and not preferable because it causes a decrease in the amount of liquid carbonic acid extracted as product liquid carbonic acid as will be described later.

The amount of liquid carbonic acid extracted from the bottom of the liquid carbonic acid rectifying column 101 is, for example, 3 mol% to 5 mol% of the amount of crude carbon dioxide supplied to the liquid carbonic acid rectifying column 101. By extracting such an amount from the bottom of the column, it becomes possible to efficiently separate high-boiling impurities contained in the crude carbon dioxide gas supplied to the liquid carbonic acid rectification column 101. As a result, high boiling impurities can be efficiently removed from the supplied crude carbon dioxide gas.

The liquid carbonic acid containing high-boiling impurities extracted from the bottom of the tower is guided to the tower bottom purging liquid carbonic acid evaporator 117 via the purge line 115.

Such a liquid carbonic acid fractionator 101 has, for example, a plurality of stages, and the number of stages of the fractionator can be set as appropriate.

The rectifying tower reboiler 103 is provided in the liquid carbonic acid rectifying column 101 and supplies a necessary amount of heat in the liquid carbonic acid rectifying tower 101. Specifically, the rectification tower reboiler 103 uses the sensible heat of the liquid refrigerant (more specifically, the pre-expansion liquid refrigerant) supplied from the refrigeration apparatus 121 described later to enter the liquid carbonate rectification tower 101. Supply the necessary amount of heat.

The first gas flow is supplied to the rectification tower top liquefier 105 out of carbon dioxide gas containing low-boiling-point impurities discharged from the top of the liquid carbonic acid rectification tower 101. In the rectifying tower top liquefier 105, heat exchange is performed between the supercooled liquid refrigerant discharged from the rectifying tower reboiler 103 and the first gas flow. As a result, in the rectification column top liquefier 105, the first gas stream is totally condensed into liquid carbonic acid. Further, as a result of the heat exchange, the liquid refrigerant becomes a gaseous state and is guided to the refrigeration apparatus 121. Further, the liquid carbonic acid obtained as a result of the condensation is guided to the rectification tower top gas-liquid separator 107 described later.

The rectifying column top gas-liquid separator 107 is a carbon dioxide gas containing liquid carbonic acid supplied from the rectifying column top liquefier 105 and low-boiling-point impurities discharged from the top of the liquid carbonic acid rectifying column 101. A second gas stream is supplied. Here, as is apparent from FIG. 1, the second gas flow is directly guided to the rectification column top gas-liquid separator 107 without passing through the rectification column top liquefier 105. The second gas flow and the liquid carbonic acid supplied from the rectification column top liquefier 105 are mixed in the rectification column top gas-liquid separator 107. As a result, flushing and reliquefaction occur in the rectification column top gas-liquid separator 107.

Here, the boiling point of carbon dioxide gas is −13 ° C. at 2.3 MPaG, whereas the boiling point of low-boiling impurities is much lower than the boiling point of carbon dioxide gas. Boiling point impurities can be sufficiently separated from liquid carbonic acid. As a result, on the liquid phase side in the rectifying column top gas-liquid separator 107, high-purity liquid carbon dioxide containing almost no high-boiling point impurities or low-boiling point impurities can be obtained.

A part of the liquid carbonic acid from which low-boiling point impurities have been removed by flashing and reliquefaction is supplied as a reflux liquid to the top of the liquid carbonic acid rectification tower 101, and the remainder is supplied to the liquid carbonic acid supercooler 109. Supplied. The amount of the reflux liquid supplied to the liquid carbonate rectification column 101 can be determined to an arbitrary value in consideration of the material balance in the impurity removal apparatus 100. For example, the rectification column top gas-liquid separator About 10 to 15% of the liquid carbonic acid discharged from 107 can be obtained.

Also, low boiling point impurities are concentrated in the gas generated in the rectification column top gas-liquid separator 107 by flash reliquefaction. Therefore, the gas enriched with the low-boiling-point impurities is discharged from the rectifying column top gas-liquid separator 107 and guided to the tower top purge gas heater 111 described later.

The liquid carbonic acid supercooler 109 is supplied with the liquid carbonic acid extracted from the rectifying column top gas-liquid separator 107. The liquid carbonate supercooler 109 exchanges heat between the liquid refrigerant supplied from the refrigeration apparatus 121 and the liquid carbonate, thereby bringing the liquid carbonate into a supercooled state to produce product liquid carbonate.

The tower top purge gas heater 111 heats the carbon dioxide gas, which is discharged from the rectification tower top gas-liquid separator 107 and concentrated with the low boiling point impurities, to room temperature. Carbon dioxide gas containing low-boiling-point impurities heated to room temperature is guided to a predetermined location through the pressure control valve 113 and is subjected to flare processing.

The pressure control valve 113 is provided in the gas line on the downstream side of the tower top purge gas heater 111. By controlling the opening / closing of the pressure control valve 113, the pressure of the entire impurity removing apparatus 100 can be adjusted. Thereby, the impurity removing apparatus 100 can maintain predetermined setting conditions (for example, 2.3 MPaG, −14 ° C.).

Further, the liquid carbonic acid extracted from the bottom of the liquid carbonic acid fractionator 101 is guided to the tower bottom purge liquid carbonic acid evaporator 117 via the purge line 115. As described above, concentrated high-boiling impurities are mixed in the liquid carbonic acid extracted from the bottom of the column.
The bottom purge liquid carbonic acid evaporator 117 vaporizes the high-boiling impurities extracted from the bottom of the liquid carbonic acid distillation column 101 to form carbon dioxide gas, and further heats to room temperature. Carbon dioxide gas containing high-boiling-point impurities heated to room temperature is guided to a predetermined location and flare-treated.

The refrigeration apparatus 121 is an apparatus that supplies and recovers the refrigerant used in the impurity removal apparatus 100. More specifically, the refrigeration apparatus 121 collects the refrigerant that has become gas as a result of the heat exchange performed in the impurity removal apparatus 100, cools the collected refrigerant to a liquid state, and then removes the impurity removal apparatus 100. To supply. The refrigeration apparatus 121 is not particularly limited, and can be used in a liquid carbonic acid production facility as long as the temperature required by the impurity removal apparatus 100 (for example, −14 ° C. to −18 ° C.) can be realized. Any refrigeration apparatus can be used. The refrigerant supplied and recovered by the refrigeration apparatus 121 can be any refrigerant that can achieve the temperature required by the impurity removal apparatus 100 (for example, −14 ° C. to −18 ° C.). For example, those having an evaporation temperature of about −30 ° C. and a condensation temperature of about 40 ° C. can be used.

The refrigerating apparatus 121 mainly includes a refrigerant compressor 123, a refrigerating machine oil separator 125, a refrigerant condenser 127, and a refrigerant liquid receiver 129, for example, as shown in FIG.

The refrigerant compressor 123 compresses the gaseous refrigerant recovered from the impurity removing device 100 and sends it to the refrigerator oil separator 125. The refrigerating machine oil separator 125 separates the refrigerating machine oil component contained in the compressed refrigerant and the gaseous refrigerant, and sends the gaseous refrigerant to the refrigerant condenser 127. The refrigerant condenser 127 condenses the gaseous refrigerant from which the refrigeration oil component has been separated into a liquid refrigerant. The refrigerant condenser 127 sends out the liquid refrigerant to the refrigerant liquid receiver 129, and the refrigerant liquid receiver 129 sends out the liquid refrigerant to the impurity removing device 100.

By using the impurity removal apparatus 100 according to the present embodiment as described above, both low-boiling impurities and high-boiling impurities in the crude carbon dioxide gas are economically removed, and the product carbon dioxide gas is recovered at a high recovery rate. Can be obtained.

The configuration of the impurity removal apparatus 100 according to the present embodiment has been described above.
Subsequently, an impurity removal method performed by the impurity removal apparatus 100 according to the present embodiment will be described in detail.

<About the removal method of impurities>
Hereinafter, the impurity removal method performed by the impurity removal apparatus 100 according to the present embodiment will be described in detail. The impurity removal method according to the present embodiment mainly includes a step of removing high boiling point impurities contained in the crude carbon dioxide gas and a step of removing low boiling point impurities from the carbon dioxide gas from which the high boiling point impurities have been removed. Prepare for.

First, a process for removing high boiling point impurities contained in the crude carbon dioxide gas will be described.

Crude carbon dioxide produced as a by-product in the refining process of natural gas or petroleum refinery gas is first supplied to the liquid carbonic acid fractionator 101. The liquid carbonic acid fractionator 101 is controlled so as to maintain a predetermined tower top temperature and pressure (for example, 2.3 MPaG, −14 ° C.). Since the column top temperature in the liquid carbonic acid rectification column 101 is equal to or higher than the boiling point of the low-boiling impurities contained in the crude carbon dioxide gas, the carbon dioxide gas contained in the crude carbon dioxide gas and the low boiling point contained in the crude carbon dioxide gas System impurities are vaporized and driven up to the top of the tower. Further, the high boiling impurities contained in the crude carbon dioxide gas are concentrated at the bottom of the liquid carbonic acid distillation column 101 because the bottom temperature in the liquid carbonic acid distillation column 101 does not reach the boiling point of the high boiling impurities. The Rukoto. Here, the amount of carbon dioxide gas that is driven up to the top of the column is, for example, 95% by volume or more and 97% by volume or less by subtracting the reflux component from the amount of crude carbon dioxide supplied to the rectifying column 101. .

Here, liquid carbonate mainly containing concentrated high-boiling-point impurities remaining in the liquid bottom at the bottom of the liquid carbonic acid rectifying column 101 is taken out of the system from the liquid carbonic acid rectifying column 101 and discharged, whereby crude carbonic acid is obtained. High boiling impurities contained in the gas can be removed.

Subsequently, a process of removing low boiling point impurities from carbon dioxide gas from which high boiling point impurities have been removed will be described.

Carbon dioxide gas discharged from the top of the liquid carbonic acid distillation column 101 is divided into two flows, a first carbon dioxide gas flow having a relatively high flow rate and a second carbon dioxide gas flow having a relatively low flow rate. The The first carbon dioxide gas flow accounts for 90 to 99% of the flow rate of the carbon dioxide gas discharged from the top of the liquid carbonic acid fractionator 101, for example. The second carbon dioxide gas flow accounts for 1 to 10% (preferably 3 to 10%) of the flow rate of the carbon dioxide gas discharged from the top of the liquid carbonic acid distillation column 101, for example. .

The first gas flow is guided to the rectification column top liquefier 105. The rectification column top liquefier 105 fully condenses the first gas stream to form liquid carbonic acid, and sends the generated liquid carbonic acid to the rectification column top gas-liquid separator 107. Further, the second gas flow is directly guided to the rectification column top gas-liquid separator 107 without passing through the rectification column top liquefier 105.

In the rectification column top gas-liquid separator 107 to which the liquid carbon dioxide generated as a result of the total condensation of the first gas stream and the second gas stream is supplied, the liquid carbon dioxide supplied from the rectification column top liquefier 105 is used. Re-flushing occurs and low boiling impurities are separated. The separated low boiling point impurities are concentrated and discharged from the rectifying tower top gas-liquid separator 107 as a gas. A gas containing low boiling point impurities is taken out of the system from the rectifying column top gas-liquid separator 107, so that the liquid carbon dioxide produced using the carbon dioxide gas from which the high boiling point impurities have been removed is further reduced. Boiling system impurities can be removed.

The liquid carbonic acid sent from the rectifying column top gas-liquid separator 107 contains almost no low-boiling-point impurities as described above, and hardly contains any high-boiling-point impurities. Part of the liquid carbonic acid sent from the rectifying column top gas-liquid separator 107 (for example, 10 mol% to 15 mol% of the number of moles of crude carbon dioxide supplied to the liquid carbonic acid rectifying column 101) Is supplied to the top of the liquid carbonic acid distillation column 101 as a reflux liquid, and is then guided to the liquid carbonic acid supercooler 109. The liquid carbonic acid supplied to the liquid carbonic supercooler 109 is taken out as product liquid carbonic acid after being brought into a supercooled state.

On the other hand, the gas enriched with low boiling point impurities discharged from the rectifying column top gas-liquid separator 107 is brought to room temperature by the tower top purge gas heater 111 and then subjected to flare treatment. In addition, since a small amount of liquid carbonic acid extracted from the bottom of the liquid carbonic acid rectification column 101 contains high-boiling impurities, it was vaporized and brought to room temperature by the column bottom purging liquid carbonic acid evaporator 117. After that, flare processing is performed.

As described above, the impurity removal method according to the present embodiment is not a method of treating raw raw carbon dioxide gas in advance with a catalyst or activated carbon. Therefore, the impurity removal method according to the present embodiment does not require heat for preheating the crude carbon dioxide gas to a temperature necessary for the catalytic reaction or heat for regenerating the activated carbon. Therefore, by using the impurity removal method according to the present embodiment, it is possible to economically remove both low-boiling impurities and high-boiling impurities in the crude carbon dioxide gas, and to obtain a product carbon dioxide gas with a high recovery rate. it can.

The impurity removal method according to this embodiment has been described above.
Hereinafter, the impurity removal apparatus and the impurity removal method according to the second embodiment of the present invention will be described in detail.

(Second Embodiment)
Subsequently, an impurity removing apparatus and an impurity removing method according to the second embodiment of the present invention will be described in detail.

When the raw material gas is natural gas or petroleum refinery gas, high-boiling-point impurities having a high melting point such as benzene and paraxylene are mixed in the crude carbon dioxide gas produced as a by-product. The crude carbon dioxide gas containing such a high-melting-point high-boiling-point impurity causes clogging of the apparatus due to precipitation of the high-melting-point high-boiling-point impurity as a solid in a low-temperature part such as a liquid carbonic acid rectification column, There is a possibility of causing a situation where continuous operation is not possible.

Therefore, the present inventors have intensively studied a method capable of preventing the occurrence of such a situation and realizing the continuous operation of the impurity removal apparatus, and in the second embodiment of the present invention described below. The inventors have come up with such an impurity removal apparatus and impurity removal method.

<About impurity removal equipment>
First, an impurity removing apparatus according to the second embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4. 3 and 4 are explanatory views for explaining the impurity removing apparatus according to the present embodiment.

For example, as shown in FIG. 3, the impurity removal apparatus 100 according to this embodiment includes a liquid carbonic acid rectification column 101, a rectification column reboiler 103, a rectification column top liquefier 105, and a rectification column top gas liquid. Separator 107, product liquid carbonate supercooler 109, tower top purge gas heater 111, pressure control valve 113, purge line 115, tower bottom purge liquid carbon dioxide evaporator 117, refrigeration apparatus 121, rectification The tower front liquefiers 151a and 151b are mainly provided.

Here, the liquid carbonate rectification tower 101, the rectification tower reboiler 103, the rectification tower top liquefier 105, the rectification tower top gas-liquid separator 107, the product liquid carbonate supercooler 109, the top purge gas according to the present embodiment. The heater 111, the pressure control valve 113, the purge line 115, the bottom purge liquid carbon dioxide evaporator 117, and the refrigeration apparatus 121 have the same configurations as those in the first embodiment of the present invention, respectively. Detailed description will be omitted to achieve the above effect.

A plurality of pre-rectification tower liquefiers 151a and 151b (hereinafter simply referred to as pre-rectification tower liquefiers 151) are installed in the impurity removing apparatus 100 according to this embodiment. In FIG. 3, only two rectification column pre-liquefiers 151 are shown, but the number of rectification column pre-liquefaction devices 151 according to this embodiment is limited to the case shown in FIG. However, three or more rectifying column pre-liquefiers 151 may be provided in the impurity removing apparatus 100.

The rectification tower pre-liquefaction device 151 is disposed on the upstream side of the liquid carbonate rectification tower 101. The rectifying column pre-liquefier 151 cools the crude carbon dioxide gas supplied to the liquid carbonic acid fractionator 101, solidifies and precipitates the high-melting-point high-boiling-point impurities contained in the crude carbon dioxide gas, and from the crude carbon dioxide gas A part of high-boiling impurities having a high melting point is removed. Here, the high-boiling impurities having a high melting point mean high-boiling impurities having a melting point higher than the top temperature of the liquid carbonic acid distillation column 101. Examples of such impurities include benzene and paraxylene. Etc.

More specifically, the rectification column pre-liquefier 151 is configured to remove crude carbon dioxide gas at a temperature lower than that of the top of the liquid carbonate rectification column 101 while maintaining the pressure (for example, 2.3 MPaG) in the impurity removal apparatus 100. (For example, about −15 ° C., which is 1 to 2 ° C. lower than the top of the column). Such temperature is a temperature at which high-boiling impurities having a high melting point are solidified but carbon dioxide gas is not solidified. Therefore, the carbon dioxide contained in the crude carbon dioxide gas passing through the pre-liquefaction tower 151 is completely condensed. It becomes liquid carbonic acid, and the high-melting-point high-boiling-point impurity contained in the crude carbon dioxide solidifies in the rectification column pre-liquefier 151 and precipitates. Thereby, the fractionator pre-liquefaction device 151 can partially remove high-melting-point high-boiling impurities from the crude carbon dioxide gas supplied to the liquid carbonate fractionator 101.

The liquid carbonic acid from which a part of the high-boiling impurities having a high melting point has been removed in this way (the crude carbon dioxide liquefied) is sent to the liquid carbonic acid distillation column 101.

In the impurity removal apparatus 100 according to the present embodiment, a continuous operation of the impurity removal apparatus 100 is realized by using a plurality of such rectification column pre-liquefiers 151. Below, the detail of the method of implement | achieving a continuous driving | operation is demonstrated, referring FIG.

FIG. 4 shows only some devices extracted from the impurity removal device 100 according to the present embodiment shown in FIG. In the description of FIG. 4, a case where there are two rectification column pre-liquefiers 151a and 151b will be described.

In the impurity removal apparatus 100 according to the present embodiment, for example, as shown in FIG. 4 (state a), the crude carbon dioxide gas is supplied to the rectification tower pre-liquefier 151a, and the rectification tower pre-liquefaction liquidator 151a is supplied. The refrigerant is supplied. In addition, the gas discharged from the tower top purge gas heater 111 is supplied to the other rectification tower pre-liquefier 151b.

Here, the rectification column pre-liquefier 151a to which the crude carbon dioxide gas is supplied is −15 ° C. under a pressure of about 2.3 MPaG (a temperature lower by 1-2 ° C. than the top temperature of the liquid carbonic acid rectification column 101). By cooling to the extent, the carbon dioxide contained in the crude carbon dioxide is fully condensed to become a liquid (liquid carbonic acid), and this liquid carbonic acid is fed to the liquid carbonic acid fractionator 101. Further, since the rectifying column pre-liquefier 151a is operated at −15 ° C. as described above, high-melting-point high-boiling impurities such as benzene and paraxylene are cooled in the rectifying column pre-liquefier 151a, Solidify and precipitate. As a result, the liquid carbonic acid rectifying column 101 is supplied with liquid carbonic acid from which a part of the high-melting-point high boiling point impurities have been removed. A few high-boiling impurities, high-boiling impurities, and low-boiling impurities are removed from the crude carbon dioxide gas by the method described in the impurity removing apparatus 100 according to the first embodiment of the present invention. . In this case, the high-melting-point high-boiling-point impurities remain slightly in the liquid carbonate rectification column 101, but the top temperature of the liquid carbonate rectification column 101 is 1 to 2 ° C. from the rectification column pre-liquefaction device 151. Because it is expensive, there is no fear of solidifying again.

If the rectifier pre-liquefier 151a is operated for a while, piping and valves are blocked by precipitation of high-melting-point high-boiling impurities such as benzene and para-xylene. Occurs and the operation of the rectifier pre-liquefier 151a becomes impossible. At this timing, as shown in FIG. 4 (state b), the flow of the crude carbon dioxide gas is switched to the other rectification tower pre-liquefier 151b in which the crude carbon dioxide gas has not flowed.

As described above, the gas discharged from the rectification column top gas-liquid separator 107 contains almost no high-boiling impurities such as benzene and paraxylene. Therefore, after this exhaust gas is returned to normal temperature by the tower top purge gas heater 111, it is supplied as a regeneration gas to the rectification tower pre-liquefier 151a on the side where the supply of the crude carbon dioxide gas is stopped due to blockage. As a result, the high-melting-point high-boiling impurities precipitated in the rectification column pre-liquefier 151a are heated by the regeneration gas at room temperature, and the solids of these high-melting-point high-boiling impurities are evaporated.・ Sublimation will occur. As a result, the high-melting-point high-boiling-point impurities present in the rectification column pre-liquefier 151a are removed from the rectification column pre-liquefaction device 151a, and the rectification column pre-liquefaction device 151a can be used again.

Thereafter, by alternately repeating this cycle using the rectification column pre-liquefiers 151a and 151b, the impurity removal apparatus 100 can be continuously operated without clogging the high melting point high boiling point impurities. Become.

As this regeneration gas, almost pure carbon dioxide gas containing a very small amount of low boiling point impurities discharged from the rectifying column top gas-liquid separator 107 is used to recover from clogging of high melting point high boiling point impurities. The inside of the rectifying column pre-liquefier 151a is filled with substantially pure carbon dioxide gas. Therefore, when the pre-rectification tower liquefier 151a recovered from the blockage of the high-melting-point high-boiling-point impurities moves to the liquefaction operation again, the liquefaction operation is resumed without using the purge gas for purging the inside of the system. Can do. By eliminating the need for such a purge gas, loss of product carbon dioxide gas can be suppressed.

The configuration of the impurity removal apparatus 100 according to the present embodiment has been described above.
In addition, the impurity removal method according to the present embodiment is such that the crude carbon dioxide gas is totally condensed by the rectification tower pre-liquefaction device 151 provided on the upstream side of the liquid carbonic acid rectification tower 101, and the high melting point contained in the crude carbon dioxide gas. Using a point where liquid carbon dioxide from which high-boiling impurities have been partially removed is supplied to the liquid carbonic acid rectification column 101 and almost pure carbon dioxide gas discharged from the rectification column top gas-liquid separator 107, The method is the same as the impurity removal method according to the first embodiment of the present invention, except that the rectification column pre-liquefaction device 151 on which high-boiling impurities are deposited is regenerated. Therefore, a detailed description of the impurity removal method according to this embodiment is omitted.

Hereinafter, an impurity removal apparatus and an impurity removal method according to an embodiment of the present invention will be described with reference to examples. However, the present invention is not limited to the following examples.

Hereinafter, the simulation result by the chemical process simulator assuming the impurity removal apparatus 100 according to the second embodiment of the present invention shown in FIG. 3 will be described in detail. The chemical process simulator used simulates the chemical process using various chemical reaction equations, physical property data, and various equations of thermodynamics, and is capable of realizing simulation in accordance with actual operation. .

The impurity removal apparatus 100 according to the second embodiment of the present invention shown in FIG. 3 includes the configuration of the impurity removal apparatus 100 according to the first embodiment of the present invention shown in FIG. It is considered preferable as an embodiment.

Example 1
[About crude carbon dioxide]
Carbon dioxide rich gas, which is a by-product gas obtained by treating natural gas by the chemical absorption method, was used as crude carbon dioxide, and the flow rate and composition of the crude carbon dioxide were set as follows. In the following, the flow rate of the crude carbon dioxide gas is indicated by both the molar flow rate (Table 1) and the mass flow rate (Table 2). This set value is based on the actual crude carbon dioxide composition. The temperature of the crude carbon dioxide gas was 20 ° C., and the pressure was 2.3 MPaG.

In Tables 1 and 2, “C2” represents a compound having 2 carbon atoms, “C3” represents a compound having 3 carbon atoms, and “C4 +” represents a compound having 4 or more carbon atoms. Represents.

[Operation conditions]
As operating conditions of the rectification column pre-liquefier 151, it is assumed that the outlet side of the rectification column pre-liquefaction device 151 is −15 ° C. and 2.3 MPaG, and is completely condensed in the rectification column pre-liquefaction device 151. .

The operating conditions of the liquid carbonic acid rectification column 101 were a rectification column having a tower diameter of 500 mm to which liquefied crude carbon dioxide gas was supplied to the bottom of the column, and the reflux liquid to the column top was 879 kg / h. The amount of carbon dioxide introduced to the top of the column was about 97% by volume of the amount of gas supplied to the liquid carbonic acid rectification column 101 by subtracting the reflux.

Of the gas discharged from the top of the liquid carbonic acid rectification column 101, 97% in the flow rate ratio is guided to the rectification column top liquefier 105 as the first gas flow, and 3% in the flow rate ratio is 3%. The gas flow was set to be directly guided to the rectification column top gas-liquid separator 107 as a gas flow of 2. The temperature of the gas discharged from the top of the tower was -13.7 ° C., and the pressure was 2.3 MPaG.

[About simulation results]
As a result of such simulation, values as shown in Tables 3 to 5 below were obtained. Table 3 shows the gas flow rate and composition on the downstream side of the tower top purge gas heater 111, and Table 4 shows the gas flow rate and composition on the downstream side of the tower bottom purge liquid carbon dioxide evaporator 117. Table 5 shows the flow rate and composition of the product liquid carbonic acid.

Note that the recovery rate of carbon dioxide in this simulation was 94.9%.

(Example 2)
A simulation was performed in the same manner as in Example 1 except that the flow rate of the second gas flow was 8%. The results obtained for the flow rate and composition of the product liquid carbonic acid are shown in Table 6.

Note that the recovery rate of carbon dioxide in this simulation was 87.7%.

(Example 3)
A simulation was performed in the same manner as in Example 1 except that the flow rate of the second gas flow was 10%. Table 7 shows the obtained results for the flow rate and composition of the product liquid carbonic acid.

Note that the carbon dioxide recovery rate in this simulation was 86.3%.

(Comparative Example 1)
A simulation was performed in the same manner as in Example 1 for the conventional impurity removal apparatus 10 shown in FIG. Table 8 shows the results obtained for the flow rate and composition of the product liquid carbonic acid.

Note that the recovery rate of carbon dioxide gas in this simulation was 94.0%.

As is clear from the above results, in Example 1 where the amount of liquid carbon dioxide purge at the bottom of the liquid carbonic acid rectification column was 3% of the mole of feed, high boiling point impurities such as benzene, toluene and xylene were already on the order of less than 1 ppm. It can be seen that it has been removed. It can also be seen that as the flow rate ratio of the second gas flow is increased, the content of low-boiling impurities is also decreased. Thus, according to the impurity removal method according to each embodiment of the present invention, it is possible to efficiently remove both high-boiling impurities and low-boiling impurities contained in the crude carbon dioxide gas, Product liquid carbonic acid can be obtained with a high recovery rate of 85% or more.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be used for the production of carbon dioxide for industrial, food and medical use, and can be used as carbon dioxide from which high-boiling impurities that affect the environment are removed even when carbon dioxide is injected into the ground. .

DESCRIPTION OF SYMBOLS 100 Impurity removal apparatus 101 Liquid carbonate rectification tower 103 Rectification tower reboiler 105 Rectification tower top liquefier 107 Rectification tower top gas-liquid separator 109 Liquid carbon dioxide supercooler 111 Tower top purge gas heater 113 Pressure control valve 115 Purge line 117 Column bottom purge liquid carbon dioxide evaporator 121 Refrigeration apparatus 123 Refrigeration compressor 125 Refrigeration machine oil separator 127 Refrigeration condenser 129 Refrigerant liquid receiver 151 Fractionator pre-liquefaction unit

Claims (9)

1. A method of removing from a crude carbon dioxide gas a high-boiling-point impurity that is an impurity having a higher boiling point than carbon dioxide gas and a low-boiling-point impurity that is an impurity having a lower boiling point than carbon dioxide gas, contained in the crude carbon dioxide gas,
   Removing the high-boiling impurities from the crude carbon dioxide gas;
   Removing the low boiling impurities from the crude carbon dioxide gas;
   Including
   The step of removing the high-boiling impurities is
   Supplying the crude carbon dioxide gas containing the high-boiling impurities and the low-boiling impurities to a liquid carbonic acid fractionator;
   A step of leading a predetermined amount of the supply amount of the crude carbon dioxide gas to the top of the column in the liquid carbonate rectification column;
   Discharging the liquid carbon dioxide containing the high-boiling impurities from the bottom of the liquid carbonic acid rectification column to the outside of the system,
   The step of removing the low boiling point impurities includes
   Splitting the carbon dioxide gas discharged from the top of the tower into a first carbon dioxide gas stream having a relatively high flow rate and a second carbon dioxide gas stream having a relatively low flow rate;
   Directing the first carbon dioxide gas stream to a rectifying column top liquefier to condense into liquid carbonic acid, and leading the liquid carbonic acid to a rectifying column top gas-liquid separator;
   Mixing the second carbon dioxide gas stream and re-flushing to separate low boiling point impurities in the liquid carbon dioxide with the rectifying column top gas-liquid separator.
2. The step of removing the high boiling point impurities further includes:
   The crude carbon dioxide gas containing the high-boiling-point impurities and the low-boiling-point impurities is supplied to any one of a plurality of rectifying column pre-liquefiers and cooled to a temperature lower than the top temperature of the column, Solidifying the high-boiling impurities having a high melting point that is higher than the top temperature of the liquid carbonic fractionator contained in carbon dioxide gas; and
   Supplying the crude carbon dioxide gas from which a part of the high-melting-point high-boiling-point impurities have been removed to the liquid carbonic acid rectification column,
   When the high-melting-point high-boiling-point impurities are blocked, the rectification column pre-liquefaction device is operated instead of the rectification column pre-liquefaction device to which the crude carbon dioxide gas is supplied, Carbon dioxide gas discharged from the liquid separator and heated to room temperature is supplied to the liquefaction column pre-liquefaction unit closed with the high melting point high boiling point impurities, and the high melting point high boiling point impurities are removed by evaporation and sublimation. The method for removing impurities in carbon dioxide gas according to claim 1.
3. The liquid carbon dioxide gas containing the high-boiling-point impurities to be raised to the top of the liquid carbonic acid rectification column is 95% or more of the supply amount of the crude carbonic acid gas by subtracting the amount returned to the liquid carbonic acid rectification column top as reflux 97 The removal method of the impurity in the carbon dioxide gas of Claim 1 or 2 which is% or less.
4. The first carbon dioxide gas flow is 90 to 99% of the flow rate of the carbon dioxide gas discharged from the top of the tower;
   The method for removing impurities in carbon dioxide gas according to any one of claims 1 to 3, wherein the second carbon dioxide gas flow is 1 to 10% of a flow rate of carbon dioxide gas discharged from the tower top.
5. The low-boiling impurities are C1-C4 alkanes, C2-C4 alkenes and C2-C4 alkynes,
   The method for removing impurities in carbon dioxide gas according to claim 2, wherein the high-boiling impurities having a high melting point are C6 or higher aromatic hydrocarbons.
6. An apparatus for removing high-boiling impurities, which are impurities having a higher boiling point than carbon dioxide gas, and low-boiling impurities, which are impurities having a lower boiling point than carbon dioxide gas, contained in the crude carbon dioxide gas from the crude carbon dioxide gas,
   The crude carbon dioxide gas is supplied, and the low-boiling point impurities contained in the crude carbon dioxide gas are led to the top of the column, and the high-boiling point impurities are concentrated to the bottom of the column,
   A rectification tower top liquefier that fully condenses a portion of the carbon dioxide gas containing the low-boiling-point impurities discharged from the top of the liquid carbonate rectification tower to form liquid carbon dioxide;
   The liquid carbonic acid liquefied by the rectification tower top liquefier and the remainder of the carbon dioxide gas containing the low-boiling impurities discharged from the top of the liquid carbonic acid rectification tower are mixed, and the low boiling point is obtained by reflashing. A rectifying column top gas-liquid separator for separating and removing system impurities;
   A purge line for discharging the concentrated high boiling point impurities out of the system from the bottom of the liquid carbonate rectification column;
   An apparatus for removing impurities in carbon dioxide gas.
7. The crude carbon dioxide gas supplied to the liquid carbonic acid rectification tower is cooled, and the high-boiling impurities having a high melting point higher than the tower top temperature in the liquid carbonic acid rectification tower contained in the crude carbonic acid gas. Further comprising a plurality of fractionator pre-liquefaction units that solidify and partially remove the high-boiling impurities having the high melting point from the crude carbon dioxide gas;
   The crude carbon dioxide gas supplied to the rectification column pre-liquefier is different from the other when the rectification column pre-liquefaction device to which the crude carbon dioxide gas is supplied is blocked by the high-melting-point high-boiling-point impurities. Is supplied to the rectification tower pre-liquefier,
   The high-melting-point high-boiling impurities deposited on the rectification column pre-liquefaction device are evaporated and sublimated by carbon dioxide gas discharged from the rectification column top gas-liquid separator and heated to room temperature. The apparatus for removing impurities in the carbon dioxide gas described.
8. The carbon dioxide gas supplied to the rectification column top liquefier is 90 to 99% of the flow rate of the carbon dioxide gas discharged from the column top,
   The carbon dioxide gas supplied to the rectifying column top gas-liquid separator is 1 to 10% of the flow rate of the carbon dioxide gas discharged from the column top, and the impurities in the carbon dioxide gas according to claim 6 or 7. Removal device.
9. The low-boiling impurities are C1-C4 alkanes, C2-C4 alkenes and C2-C4 alkynes,
   The apparatus for removing impurities in carbon dioxide gas according to claim 7, wherein the high-boiling impurities having a high melting point are C6 or higher aromatic hydrocarbons.

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