JP2004250240A - Manufacturing method and manufacturing apparatus for liquefied carbon dioxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method and manufacturing apparatus which suppress the concentration of carbon monoxide in a gaseous phase generated by the vapor-liquid equilibrium of the obtained liquefied carbon dioxide to a lower level even when gaseous carbon dioxide containing the gaseous hydrogen and gaseous carbon monoxide as impurities is used as a gaseous raw material. <P>SOLUTION: The liquefied carbon dioxide of ≤1 vol. ppm in a carbon monoxide content in the gaseous phase generated by the vapor-liquid equilibrium is obtained by compressing the gaseous raw material containing the carbon monoxide and hydrogen as the impurities in the gaseous carbon dioxide, then causing the oxidation reaction thereof while regulating the amount of oxygen supply in such a manner that the range of temperature rise attains 3 to 20°C, then liquefying the reaction product. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for producing liquefied carbon dioxide.
[0002]
[Prior art]
Generally, liquefied carbon dioxide is produced by a process as shown in FIG. First, the carbon dioxide gas a as a raw material is compressed by the compressor 1 from 2 to 5 kPa to about 2000 to 2500 kPa. Since the temperature of the compressed gas b obtained at this time has risen to about 100 ° C., it is sent to the precooler 3 and cooled to 10 ° C. or less. The cooled cooling gas d is sent to the processing device 4 to remove adsorptive impurities such as odor components and water. Then, the obtained processing gas e is introduced into the liquefier 5 to be liquefied. At this time, the non-adsorbing impurity gas g such as methane and hydrogen having a low condensation temperature is discharged out of the system. The obtained liquefied carbon dioxide f is stored in the tank 6 and transported and used for various uses.
[Problems to be solved by the invention]
[0003]
By the way, as the carbon dioxide gas a as a raw material, a carbon dioxide gas generated in a steam reforming step performed in an ammonia production step or the like may be used. Hydrogen gas or carbon monoxide gas may be contained as impurities in the carbon dioxide gas generated in the steam reforming step. Among them, hydrogen gas can be separated in the liquefaction step by the liquefier 5 described above, but carbon monoxide is easily mixed into the product. For this reason, the concentration of carbon monoxide in the gas phase generated by the vapor-liquid equilibrium of the obtained liquefied carbon dioxide may increase.
[0004]
Therefore, the present invention provides a method for producing a carbon dioxide gas in a gaseous phase produced by a vapor-liquid equilibrium of liquefied carbon dioxide obtained even when a carbon dioxide gas containing hydrogen gas or carbon monoxide gas as an impurity is used as a raw material gas. It is intended to suppress the amount of the low.
[0005]
[Means for Solving the Problems]
The present invention compresses a raw material gas containing carbon monoxide and hydrogen as impurities in carbon dioxide gas, and then performs an oxidation reaction while adjusting the oxygen supply amount so that the temperature rise ranges from 3 to 20 ° C. And then liquefaction, so that the carbon monoxide content in the gas phase produced by vapor-liquid equilibrium is 1 vol. The above problem was solved by obtaining liquefied carbon dioxide having a concentration of not more than ppm.
[0006]
Oxygen is added to the raw material gas under predetermined conditions and compressed to oxidize carbon monoxide in the raw material gas, so that the carbon monoxide content in the liquefied gas can be further reduced. Therefore, the carbon monoxide content in the obtained liquefied carbon dioxide can be reduced, and the carbon monoxide content in the gas phase generated by the vapor-liquid equilibrium of the liquefied carbon dioxide can be suppressed.
[0007]
Also, since the source gas contains hydrogen, even if oxygen is added in an amount that can completely oxidize carbon monoxide, the remaining oxygen is used for reaction with hydrogen, and the oxygen concentration in the resulting liquefied carbon dioxide Can also be lower.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The method for producing liquefied carbon dioxide according to the present invention is a method for producing by compressing a raw material gas A mainly composed of carbon dioxide gas, then performing an oxidation reaction, and then liquefying.
[0009]
The source gas A is a gas containing carbon dioxide gas as a main component and carbon monoxide and hydrogen as impurities. Examples of such a raw material gas A include carbon dioxide gas generated in a steam reforming process performed in an ammonia production process or the like.
[0010]
The content of carbon monoxide in the raw material gas A is 10 to 1000 vol. ppm is good, and 10 to 100 vol. ppm is preferred. The carbon monoxide content is 10 vol. ppm, but may be less than 10 ppm by volume of carbon dioxide gas generated in the steam reforming step. Those less than ppm are difficult to obtain. On the other hand, when the carbon monoxide content is 1000 vol. If the amount is more than ppm, a large amount of oxygen is required to sufficiently oxidize carbon monoxide by the above oxidation reaction, and there is a possibility that residual oxygen may be mixed into liquefied carbon dioxide of the product. Further, if the amount of supplied oxygen is adjusted so that the amount of residual oxygen does not occur in the oxidation reaction, carbon monoxide cannot be sufficiently oxidized, and there is a possibility that the remaining carbon monoxide may be mixed into the liquefied carbon dioxide of the product. is there.
[0011]
The content of hydrogen in the raw material gas A was 1000 vol. ppm to 1 vol% is good and 3000 vol. ppm to 1 vol% is preferred. When the hydrogen content is more than 1 vol%, the yield of the obtained liquefied carbon dioxide is affected. On the other hand, when the hydrogen content is 1000 vol. If the amount is less than 1 ppm, the amount of hydrogen oxidized together with the carbon monoxide in the above oxidation reaction decreases, and even if an oxygen supply amount described later is adjusted, oxygen remains, and the residual oxygen is liquefied. There is a risk of mixing in carbon dioxide. Further, when the oxygen supply amount is further reduced so that oxygen does not remain in the liquefied carbon dioxide of the product, it may be difficult to adjust the preferable oxygen supply amount.
[0012]
The content ratio of carbon monoxide and hydrogen contained in the raw material gas A is preferably hydrogen / carbon monoxide = 100 to 1000 (volume ratio), and more preferably 300 to 1,000. If the content ratio is smaller than 100, oxygen may remain in the above-mentioned oxidation reaction even if the supply amount of oxygen described below is adjusted, and the remaining oxygen may be mixed into the liquefied carbon dioxide of the product. Further, when the oxygen supply amount is further reduced so that oxygen does not remain in the liquefied carbon dioxide of the product, it may be difficult to adjust the preferable oxygen supply amount. On the other hand, when the content ratio is larger than 1000, the yield of the obtained liquefied carbon dioxide is affected.
[0013]
The compression step is a step of applying a pressure necessary for liquefying the carbon dioxide gas by the liquefaction, and compresses the raw material gas A of 2 to 5 kPa to about 2000 to 2500 kPa. The temperature of the compressed gas B obtained in this step is raised to 90 to 110 ° C.
[0014]
The oxidation reaction step is a step of oxidizing carbon monoxide in the compressed gas B to carbon dioxide with oxygen. At this time, the oxygen supply amount is determined by the difference between the temperature of the compressed gas B introduced into the oxidation reaction step and the temperature of the oxidizing gas C obtained by the oxidation reaction, that is, the range of the temperature increase due to the oxidation reaction step. Is preferably adjusted to 3 to 20 ° C, and more preferably to 3 to 10 ° C. If the temperature difference is less than 3 ° C., oxygen cannot be supplied sufficiently, and carbon monoxide in the compressed gas B may not be sufficiently oxidized. On the other hand, if it is higher than 20 ° C., oxygen may remain in the resulting oxidized gas C and oxygen may remain in the liquefied carbon dioxide of the product.
[0015]
In this oxidation reaction step, there is no particular limitation as long as the catalyst can oxidize carbon monoxide, and any catalyst such as a platinum catalyst or a platinum-containing catalyst can be used. When the oxidation reaction step is a continuous reaction, the efficiency can be further improved by supporting the catalyst on a carrier. Examples of such a carrier include silica gel, molecular sieve, cordierite, and alumina.
[0016]
The carbon monoxide content in the oxidized gas C obtained by the oxidation reaction step is 5 vol. ppm or less and 1 vol. ppm or less is preferred. By satisfying this, the content of carbon monoxide in the gas phase generated by the vapor-liquid equilibrium of liquefied carbon dioxide in the obtained product is 1 vol. ppm or less. In addition, since the carbon monoxide in the obtained oxidized gas C does not need to be present, its content is 0 vol. ppm.
[0017]
The carbon monoxide content in the gas phase produced by the vapor-liquid equilibrium of liquefied carbon dioxide in the resulting product is 1 vol. ppm or less is preferred. Carbon monoxide is a toxic substance, 1 vol. If it is higher than ppm, it is not preferable when used for food applications and the like.
[0018]
The above-mentioned gas-liquid equilibrium means a phase equilibrium between a liquid phase and a gaseous phase, specifically, in the case of liquefied carbon dioxide, refers to a phase equilibrium between liquefied carbon dioxide and carbon dioxide gas obtained by gasifying the same. The vapor-liquid equilibrium is influenced by the composition of one phase, for example, liquefied carbon dioxide, and the composition of the other phase, for example, carbon dioxide gas. That is, when the carbon monoxide content in the liquefied carbon dioxide on the liquid phase side decreases, the carbon monoxide content in the carbon dioxide gas on the gas phase side decreases. For this reason, by reducing the carbon monoxide content in the liquefied carbon dioxide on the liquid phase side, the carbon monoxide content in the carbon dioxide gas on the gas phase side can be reduced.
[0019]
The oxidizing gas C thus obtained is cooled to 10 ° C. or lower, preferably 0 to 10 ° C., and then polar gases such as ammonia and water are removed by various adsorbents. By liquefying by lowering the temperature to 20 ° C., liquefied carbon dioxide can be obtained.
[0020]
Next, an apparatus for producing liquefied carbon dioxide used in the above production method will be described.
As shown in FIG. 1, the apparatus for producing liquefied carbon dioxide according to the present invention includes a compressor 11, an oxidation reactor 12, a precooler 13, a removing device 14, a liquefier 15, and a tank 16.
[0021]
The compressor 11 is a device that compresses the raw material gas A having a pressure of 2 to 5 kPa to 2000 to 2500 kPa to produce a compressed gas B. When the compressed gas B is cooled by the liquefier 15, the carbon dioxide gas is liquefied. It gives pressure. The temperature of the compressed gas B obtained at this time is raised to 90 to 110 ° C.
[0022]
The oxidation reactor 12 is a device for oxidizing carbon monoxide in the compressed gas B with oxygen, and an oxidation reaction is caused by the catalyst filled therein. Thereby, the content of carbon monoxide was reduced to 5 vol. ppm or less.
[0023]
The amount of oxygen supplied to the oxidation reactor 12 is such that the difference between the temperature of the compressed gas B and the temperature of the oxidizing gas C discharged from the oxidation reactor 12 is 3 to 20 ° C, preferably 3 to 10 ° C. Adjustment mechanism. As such an adjusting mechanism, each temperature sensor provided in the compressed gas B introduction part and the oxidation processing gas discharge part of the oxidation reactor 12, a determination device for processing and determining data measured by both temperature sensors, and A combination of a pneumatic control valve for opening and closing the oxygen supply line by the determination device may be used.
[0024]
The precooler 13 is a device for cooling the oxidizing gas C discharged from the oxidizing reactor, and reduces the temperature of the oxidizing gas C raised by the compression and oxidation reaction to 10 ° C. or less, preferably 5 to 8 ° C. It is a device that cools to ℃. Thus, the amount of water brought into the dryer 14b can be reduced.
[0025]
The removal device 14 is a device that removes adsorptive impurities contained in the cooling gas discharged from the precooler 13, and includes, for example, a deodorizer 14a that removes a polar gas such as ammonia, and a dryer 14b that removes water. Or a combination thereof.
[0026]
The liquefier 15 is a device that liquefies the processing gas E discharged from the removing device 14 to liquefy carbon dioxide, lowers the temperature of the processing gas E to −20 ° C., and liquefies the carbon dioxide gas. Let it.
[0027]
The obtained liquefied carbon dioxide F is stored in the tank 16, taken out, used, or transported. Further, the impurity gas G such as methane and hydrogen which has not been liquefied by the liquefier 15 is discharged out of the system.
[0028]
Since only the liquefied carbon dioxide F is present in the tank 16, the liquefied carbon dioxide F is in a gas-liquid equilibrium state in the tank 16, and a gas phase is generated. Since the amount of carbon monoxide in the gas phase has been reduced by the oxidation in the oxidation reactor 12, 1 vol. ppm or less.
[0029]
The liquefied carbon dioxide thus obtained can be used for beverages, cooling, and the like.
[0030]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0031]
[Method for analyzing carbon dioxide gas]
After sampling, the components were measured by gas chromatography.
[0032]
(Example 1)
Using a test machine having the flow shown in FIG. 3, a 1 / 30th scale reactor of the actual machine was installed, and an oxidation removal test of carbon monoxide and hydrogen in the raw carbon dioxide gas was performed. Specifically, the raw material gas is extracted from the intermediate stage of the compressor 11, the flow rate is measured using the flow meter 21 at about 240 to 270 kPa, and is passed through the preheater 22 together with the oxygen gas whose flow rate has been measured. After the temperature was increased, a platinum catalyst (platinum loading: 0.27% by weight, simple substance: cordierite + alumina coating, manufactured by Sudo Chemie Catalyst Co., Ltd .; N-220 honeycomb) was filled in two blocks (150 square × 50H / block). After passing through the reactor 23, the composition was measured by a thermometer 24 before and after the reactor 23, and the composition of the outlet gas from the reactor 23 was measured by a gas chromatograph 25 and compared with the composition of the raw material carbon dioxide gas. The results are shown in FIGS.
[0033]
[result]
4 to 6, in the reactor, the oxidation reaction rate of carbon monoxide (CO) reaches almost 100% even if the oxygen concentration at the inlet is relatively low, but since the concentration of hydrogen is higher than that of CO, The reaction rate does not reach 100% unless the inlet oxygen concentration is increased to about 3500 ppm. On the other hand, it can be seen that the temperature difference (ΔT) between the inlet and outlet of the reactor increases with the reaction rate of hydrogen. In addition, it can be seen that as the reaction rate of hydrogen increases, the amount of oxygen that does not contribute to the reaction gradually increases.
[0034]
FIG. 7 shows the results of investigating the reactor inlet temperature required to start the oxidation reaction under the catalyst used by CO for the test. As can be seen from this, it is understood that a temperature of 80 ° C. or higher is preferable in order to maintain the reaction rate of 90%.
[0035]
From these results, it is understood that the amount of oxygen needs to be controlled to an appropriate amount for the CO oxidation reaction. If oxygen is introduced excessively for the reaction, unreacted oxygen may flow into the product system, possibly exceeding the oxygen concentration standard of the product liquefied carbon dioxide gas, which is a problem.
[0036]
【The invention's effect】
According to the present invention, oxygen is added to the raw material gas under predetermined conditions and compressed to oxidize carbon monoxide in the raw material gas, so that the carbon monoxide content in the liquefied gas can be further reduced. Thereby, the carbon monoxide content in the obtained liquefied carbon dioxide can be reduced, and the carbon monoxide content in the gas phase generated by the vapor-liquid equilibrium of the liquefied carbon dioxide can be suppressed.
[0037]
Also, since the source gas contains hydrogen, even if oxygen is added in an amount that can completely oxidize carbon monoxide, the remaining oxygen is used for reaction with hydrogen, and the oxygen concentration in the resulting liquefied carbon dioxide Can also be lower.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an apparatus for producing liquefied carbon dioxide according to the present invention. FIG. 2 is a schematic view showing an example of a conventional apparatus for producing liquefied carbon dioxide. FIG. 3 is a test apparatus used in Example 1. FIG. 4 is a graph showing the results of Example 1 (inlet oxygen concentration and reaction rate). FIG. 5 is a graph showing the results of Example 1 (reactor ΔT and reaction rate). FIG. 6 is an example. 1 is a graph showing the results (inlet oxygen concentration and residual oxygen concentration) of FIG. 1. FIG. 7 is a graph showing the results of Example 1 (reaction temperature and CO conversion).
1,11 Compressor 2,12 Oxidation reactor 3,13 Precooler 4,14 Removal device 14a Deodorizer 14b Dryer 5,15 Liquefier 6,16 Tank 21 Flow meter 22 Preheater 23 Reactor 24 Thermometer 25 Gas chroma Graph a Carbon dioxide gas A Raw material gas b, B Compressed gas C Oxidizing gas d, D Cooling gas e, E Processing gas f, F Liquefied carbon dioxide g, G Impurity gas

Claims (6)

A raw material gas containing carbon monoxide and hydrogen as impurities in carbon dioxide gas is compressed, and then an oxidation reaction is performed while adjusting an oxygen supply amount so that a temperature rise range is 3 to 20 ° C., and then liquefaction is performed. As a result, the carbon monoxide content in the gas phase generated by the gas-liquid equilibrium is 1 vol. A method for producing liquefied carbon dioxide, wherein liquefied carbon dioxide having a concentration of not more than ppm is obtained. The content of the carbon monoxide is 10 to 1000 vol. The method for producing liquefied carbon dioxide according to claim 1, wherein the concentration is ppm. The method for producing liquefied carbon dioxide according to claim 2, wherein the content ratio of carbon monoxide and hydrogen contained in the raw material gas is hydrogen / carbon monoxide = 100 to 1000 (volume ratio). The content of hydrogen is 1000 vol. The method for producing liquefied carbon dioxide according to claim 3, wherein the content is from ppm to 1 vol%. A compressor for compressing a raw material gas containing carbon monoxide and hydrogen as impurities in carbon dioxide gas, an oxidation reactor for oxidizing carbon monoxide in the compressed raw material gas, and an oxidation treatment discharged from the oxidation reactor It has a precooler for cooling the gas, a removing device for removing adsorbable impurities contained in the cooling gas discharged from the precooler, and a liquefier for liquefying the processing gas discharged from the removing device to liquefy carbon dioxide. Liquid carbon dioxide production equipment. 6. The oxygen reactor according to claim 5, wherein the oxidation reactor has an oxygen supply amount adjusting mechanism such that a difference between the temperature of the raw material gas introduced here and the temperature of the oxidation processing gas discharged therefrom is 3 to 20 ° C. The apparatus for producing liquefied carbon dioxide according to the above.

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