JPH05124808A - Treatment of gaseous raw material in purification plant of high-purity gaseous carbon dioxide - Google Patents

Abstract

PURPOSE:To stably maintain the purity of a gaseous carbon dioxide product at high degree by regulating the temperature and the pressure in a hydrocracking stage to the specified range in the preliminary treatment stage of crude gaseous carbon dioxide. CONSTITUTION:Crude gaseous carbon dioxide is obtained by treating gaseous carbon dioxide contained in combustion exhaust gas discharged from a boiler or the like by a pressure fluctuation adsorption method. Then, before this gaseous carbon dioxide is purified into high-purity gaseous carbon dioxide by a liqucfaction distillation purification equipment being in a compression state, the following treatment is performed. In other words, the crude gaseous carbon dioxide is preliminarily compressed at 3-5kg/cm<2> G and introduced into a tower packed with a catalyst for hydrocracking and hydrocracked in the conditions of 60--100 deg.C. Then the hydrocracked substance is pressurized at 15-20-kg/cm<2> G to remove moisture and odorous matter. Thereafter. the same is cooled at the saturation temperature or below of gaseous carbon dioxide and supplied to the liquefaction distillation purification equipment. By this treatment of the gaseous raw material, as pretreatment for introducing the crude gaseous carbon dioxide into the liquified carbon dioxide purification plant, not only deoxygenation but also decomposition of nitrogen oxide are completely performed and also deterioration of activity of a catalyst is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention separates carbon dioxide gas (hereinafter referred to as CO ₂ ) from combustion exhaust gas from a boiler or the like to obtain crude CO ₂ and then uses it as a raw material gas for a high-purity CO ₂ liquefaction production plant. Pretreatment method.

[0002]

_2. Description of the Related Art Separation and purification of CO ₂ from a CO ₂ -containing gas by a pressure swing adsorption (PSA) apparatus is carried out by separating CO ₂ from the CO ₂ -containing gas disclosed in JP-A-61-157322. It is known as a method of concentrating.

Further, a method for separating and purifying CO ₂ from combustion exhaust gas from a boiler or the like using a PSA device or the like is also disclosed in Japanese Patent Laid-Open No.
-290517 (Method and apparatus for processing raw material gas in high-purity liquefied carbonic acid refining plant).

Liquefied carbonic acid used in the food and drink industry is
CO ₂ 99.9%, NO 5pp as food hygiene law standards
Below m, NO ₂ , SO ₂ , H ₂ S, CO, etc. are defined as traces (trace amount). By the way, in the crude CO ₂ obtained by separating CO ₂ from the combustion exhaust gas from a boiler or the like with a PSA device, NO, NO _{2 and the} like considerably remain in addition to O ₂ , and the crude CO ₂ enters the high-purity liquefied carbon dioxide purification device. NO before
_{Even if 2} is removed, NO ₂ is produced by the reaction between residual O ₂ and NO, and this NO ₂ migrates to the liquefied CO ₂ side, which causes the quality of the product liquefied carbonic acid to deteriorate.

Therefore, one of the applicants of the present application has previously disclosed, in Japanese Patent Laid-Open No. 1-290517, a deoxidizer for removing O ₂ contained in crude carbon dioxide gas in advance on the upstream side of the dehumidifier. In this way, a method has been proposed in which the oxygen content in the crude carbon dioxide gas sent to the liquefied carbon dioxide refining device is reduced to reduce the amount of nitrogen oxides transferred to the liquid phase side.

This method uses a compressor of 15 kg / cm.
Increase the pressure to about ² and set the internal temperature of the deoxidizer filled with a metal catalyst such as Pt or Ni to about 40 ° C.
₂ is introduced, O ₂ contained in the crude carbon dioxide gas is reacted with H _{2 by} the action of the metal catalyst, and is converted into H ₂ O by the subsequent dehumidifier.

[0007]

In the above method, the O ₂ contained in the crude carbon dioxide gas is surely removed as water vapor H ₂ O, but nitrogen oxides such as NO and NO ₂ are not completely removed. Cannot be removed. Furthermore, the pressure after the compressor is 15 kg.
/ Cm ² , under the conditions of the deoxidizer internal temperature of about 40 ℃,
The generated water vapor H ₂ O is liquefied below the dew point to Pt, Ni
It has been found that the metal catalyst activity of such as is likely to decrease.

An object of the present invention is not only deoxidation but also pretreatment for charging crude carbon dioxide gas to a liquefied carbon dioxide refining apparatus.
Completely decomposes nitrogen oxides such as NO and NO ₂ ,
An object of the present invention is to provide a pretreatment method that does not reduce the catalytic activity.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have used a hydrocracking catalyst to control pressure and temperature conditions within specific ranges. As a result, they have found that not only the catalyst activity can be prevented from being lowered, but also nitrogen oxides such as NO and NO ₂ can be completely decomposed as well as deoxygenation.

That is, according to the present invention, carbon dioxide gas contained in combustion exhaust gas from a boiler or the like is treated by a pressure fluctuation adsorption method to obtain crude carbon dioxide gas, which is then purified by a liquefied distillation purification apparatus under a compressed state. Prior to purification into gas, the crude carbon dioxide gas was precompressed to a pressure of 3 to 5 kg / cm ² G, charged into a hydrocracking catalyst packed column, and the temperature was 60 ° C. or higher and 10
Hydrocracked under 0 ℃ or less, then 15-20kg
Of the raw material gas in a high-purity carbon dioxide refining plant characterized by supplying water to a liquefaction distillation refining equipment by pressurizing to / cm ² G to remove water and odor and then cooling to a temperature below the saturation temperature of carbon dioxide. It is a processing method.

The details will be described below. The gas burned in the boiler combustion furnace is not particularly limited, but in addition to petrochemicals, off-gas of petroleum refining plants, etc., converter gas (LDG), blast furnace gas (BFG), coke oven gas ( COG), lime furnace gas, etc. are available,
Particularly preferred is L, which has a high carbon dioxide concentration in the combustion exhaust gas.
It can be preferably used for CO ₂ recovery from DG boiler exhaust gas.

The exhaust gas branched from the boiler exhaust gas line is treated by a CO ₂ separation device by the PSA method, and the PSA method in this case is described in the above-mentioned JP-A-61-15732.
The method of the CO ₂ / PSA process described in Japanese Patent Publication No. 2 (method of separating and concentrating CO ₂ from CO ₂ containing gas) can be used.

The principle of this CO ₂ / PSA process is generally a PSA system of the type in which one column is adsorbed under normal pressure while the other is vacuum desorbed by the alternating switching system by the A and B double column system. Therefore, each tower can be filled with activated carbon or the like as an adsorbent and used. At this time, the tower A follows the time schedule of pressurization-adsorption-washing-desorption, while the tower B follows the time schedule of desorption-pressurization-adsorption-washing. In such CO ₂ / PSA process, a PSA for recovery and purification of CO ₂ is adsorbed components, in order to increase the purity of the product CO _2, using a portion of the product CO _2, co-adsorbed components (N ₂₎ It is necessary to wash (purge).

When the purified CO ₂ gas discharged from the PSA process is to be further purified, it is purified by distillation in a liquefaction purification apparatus after being prepressurized to a pressure required to maintain a predetermined liquefaction temperature with a compressor. Usually, as a pretreatment of this liquefaction refining apparatus, a crude CO ₂ gas is charged with a deoxidizer tower filled with a metal catalyst, zeolite, etc., and a dehumidifier excluding H ₂ O, activated carbon, etc., and H ₂ S , SO ₂ , NO _{2 and} other deodorization towers are pretreated.

In this case, NO in the exhaust gas, which is the raw material,
When NOX (nitrogen oxide) such as NO ₂ is contained,
NO ₂ can be adsorbed and removed in the deodorization tower, and can also be removed in the washing tower because it has reactivity with water, but since NO has low adsorbability to the adsorbent and does not have high solubility in water, the deodorization tower Also, it is difficult to remove it with a washing tower. Moreover, this NO reacts with the residual O ₂ in the liquefaction refining device to become NO ₂ , which moves to the liquid phase side and deteriorates the quality of the purified carbon dioxide gas.

In the present invention, therefore, not only oxygen but also NO, NO _{2 and the} like are hydrocracked in a column packed with a metal catalyst for hydrocracking, and the produced H ₂ O is condensed to lower the catalytic activity. Set a condition that does not exist. That is, the crude CO ₂ gas is pre-compressed to a pressure of about 3 to 5 kg / cm ² G to obtain Pt, N
In a packed column of a metal catalyst for hydrocracking such as i, the catalyst layer is hydrocracked under the conditions of a temperature of the catalyst layer of 60 ° C. or higher and 100 ° C. or lower,
Next, the pressure is raised to 15 to 20 kg / cm ² G to remove water and odor, and then the temperature is cooled to the saturation temperature of CO ₂ or lower and supplied to the liquefaction distillation purification device. This hydrogenolysis is O ₂ is H
₂ O, NO and NO ₂ decompose into N ₂ and H ₂ O. In addition, a desulfurization tower filled with activated carbon is provided in front of the hydrocracking tower to reduce SO ₂ and H
_It is desirable to remove ₂ S, etc.

In the hydrocracking tower, a temperature of 60 ° C. or higher, 10
The reason for limiting the temperature to 0 ° C or lower is that when the temperature is lower than 60 ° C, N
It is difficult for hydrogenolysis of nitrogen oxides such as O and NO ₂ to occur, and at the same time, depending on the outside temperature and the amount of water in the system, condensed water is generated near the dew point of water, and the catalytic activity is likely to decrease. .. On the other hand, if the temperature exceeds 100 ° C., NH ₃ is generated by hydrogenation of nitrogen oxides, which is mixed as an impurity in liquefied CO ₂ obtained by the liquefaction distillation purification device, which causes an unpleasant odor.

If the pressure is also less than 3 kg / cm ² G, the hydrogenolysis of nitrogen oxides of NO and NO ₂ is less likely to occur in the above temperature range, and if the pressure is more than 5 kg / cm ² G, the above temperature is exceeded. In the range, NH ₃ is easily generated, which is not preferable.

The crude CO ₂ gas leaving this hydrocracking tower is then pressured by the compressor to maintain a predetermined liquefaction temperature, for example 16 kg / cm ² at a liquefaction temperature of -30 ° C.
G is subjected to a preliminary treatment such as a dehumidifier filled with zeolite or the like and a deodorizing tower filled with activated carbon or the like after being compressed so as to be 19 kg / cm ² G at a liquefaction temperature of -20 ° C. The dehumidifier is dehumidified until the dew point reaches about -60 ° C. In the deodorization tower, hydrogen sulfide, ammonia, etc. are removed.

Next, CO is fed by a refrigerator using CFC gas or the like.
_After condensing and liquefying ₂ below the saturation temperature, it is supplied to a liquefaction distillation purification device to separate and remove N ₂ -based inert gas from the upper part of the distillation column, and purified liquefied CO from the lower part of the column.
You can get ₂ .

[0021]

The present invention uses crude C as a pretreatment for the liquefaction purification apparatus.
In a hydrocracking device filled with O ₂ gas with a metal catalyst, NO, NO is generated by hydrocracking under specific temperature and pressure conditions.
Nitride oxide such as ₂ to N ₂ and H ₂ O, and converts oxygen into H ₂ O, yet moisture condenses in the catalyst layer since conventional is also low, at higher temperatures oxygen column, decreased activity Since NO, NO ₂ , NH _{3 and the} like do not flow into the liquefaction refining apparatus without causing the occurrence, it is possible to obtain purified liquefied CO ₂ that is suitable for food and drink without impurities such as NO ₂ and NH _3. it can.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Example 1) (Comparative Example 1) O _{2 in the} CO ₂ gas: 200 ppm, NO: 170 ppm, N
O ₂ : 3.0 ppm in the raw material gas containing H ₂ : 700 pp
m was added, the pressure of the reaction column filled with the platinum catalyst and the temperature of the catalyst layer were changed as follows, and the mixture was allowed to flow at SV = 5000, and the outlet gases O ₂ , NO, NO ₂ , and NH ₃ were analyzed. did. The analysis method is O ₂ , H ₂ is gas chromatography, N is
Absorption spectrophotometry was used for O, NO ₂ , and NH ₃ . The results are shown in Table 1. The inside of the central frame is an example, and the periphery is a comparative example.

[0023]

[Table 1]

(Example 2) (Comparative Example 2) The flow diagram of FIG. 2 shows Comparative Example 2 in which the deoxidizing tower 26 is provided in the conventional carbon dioxide gas pretreatment step.
In FIG. 2, 21 is a converter gas (LDG) combustion boiler, and 22 is the LDG combustion gas. 23 is P
SA device, and 24 is a crude carbon dioxide gas. This was compressed to 16 kg / cm ² G with a compressor 25 and charged into a deoxidizer 26, while H ₂ gas was charged and the temperature was 40 ° C.
Is contacted with a Pt catalyst to convert O ₂ into H ₂ O.

Under this condition, the temperature is low, so O ₂ is 1 ppm.
Although it decreased to below, although NO depends on the amount of hydrogen, 40 to 50 ppm of NO remains with the amount of hydrogen that suppresses the generation of NH ₃ , and NO is not removed by the dehumidifier 28 and the deodorizer 30, so it is liquefied. It enters the distillation / purification unit 32, where most of it is separated into the offgas at the top of the column. In this case O ₂ is a reaction of the NO and O ₂ at the top part when the remaining, NO ₂ is produced, but mixed in the product liquefied carbon dioxide bottoms, O ₂ is sufficiently removed even by the conventional apparatus of FIG. 2 If this is not the case,
NO ₂ in the product was kept below 1 ppm.

However, at some time, the temperature rise due to the reaction heat of this deoxidation tower disappears, and NOX in the product CO ₂ is 30 to 30%.
It rose to 40ppm. That is, it was determined that the catalytic function of the deoxidizer was lost. As a result of the investigation, it was determined that H ₂ O converted into O ₂ had a low reaction temperature and was concentrated in the deoxidation tower due to the high pressure to lose the catalytic function. However, if the temperature is raised at this pressure, the amount of NH ₃ produced increases due to the effect of H ₂ O produced by the reaction, and there is a problem that NH ₃ cannot be completely removed even if deodorized with activated carbon in the deodorization tower. It happens. Therefore, there is no generation of NH ₃ and O ₂ , NO, NO ₂
It is the present invention to find out the conditions for hydrocracking which can be simultaneously removed.

FIG. 1 is a flow diagram embodying the method of the present invention. 1 is a combustion boiler converter gas (LDG), but the NO ₂ in the combustion gas 2 are removed NO ₂ provided de NO ₂ column for the adsorbent protection such as activated carbon of PSA device, flows Illustration is omitted. NO gas cannot be removed. Next, carbon dioxide is adsorbed and separated by the PSA device 3. 4 is a crude CO ₂ gas.

This gas is supplied to the compressor 3 to
The pressure is increased to 5 kg / cm ² G, and the hydrocracking tower 8 is charged into the desulfurization tower 6 for protecting the catalyst. This desulfurization crude CO ₂ gas is
It is charged into a hydrocracking tower together with H ₂ gas at a temperature of 60 to 100 ° C. As the catalyst, a platinum-based catalyst, a palladium-based catalyst or the like could be used. Here, O ₂ is H ₂ O and NO is N
₂ and H ₂ O, and NO ₂ is also decomposed into N ₂ and H ₂ O. Since the temperature is higher and the pressure is lower than before, condensation of steam in the column does not occur and the catalyst activity can be maintained for a long time. Since the pressure is low, NH ₃ is not generated and the burden on the subsequent deodorization tower is lightened.

The gas 9 leaving the hydrocracking tower is pressurized by a compressor 10 to a pressure of 15 to 20 kg / cm ² G required to maintain a predetermined liquefaction temperature, and passes through a dehumidifier 11 filled with zeolite. After removing the water content, a small amount of residual SO ₂ , H ₂ S,
After removing NO _{2 and the} like, the liquefied raw material gas 14 is charged into the liquefaction distillation purification device 15. From the top of the column, most of the N ₂ gas is removed as the off-gas 17, and the rest is a slight amount of NO gas. Target liquid carbon dioxide gas from the bottom of the tower 16
Pull out. This liquefied carbon dioxide gas is 99.9% CO ₂ .
Above, dew point -60 ℃ or less, NO 0.1ppm or less, SO
₂ , H ₂ S, NO ₂ and CO were all traces and satisfied the Food Sanitation Law standards.

[0030]

EFFECT OF THE INVENTION In the pretreatment process of crude carbon dioxide gas, the temperature of the hydrocracking process is set to 60 to 100 ° C. and the pressure is set to 3 to 5 kg.
/ Cm ² G prevents the generated water vapor from condensing in the tower, decomposes NO and NO ₂ almost completely, and
_Since the generation of ₃ could be suppressed, the burden on the subsequent deodorization tower was reduced, and the amount of NO entering the liquefaction distillation purification device could be made extremely small, and the purity of the product carbon dioxide gas could be stably maintained at a high level. Made it possible.

[Brief description of drawings]

FIG. 1 is a flow diagram of a high-purity carbon dioxide purification plant of the present invention.

FIG. 2 is a flow diagram of a conventional carbon dioxide refining plant.

[Explanation of symbols]

1 Converter Gas Combustion Boiler 2 LDG Combustion Gas 3 PSA Device 4 Crude Carbon Dioxide 5 Compressor 6 Desulfurization Tower 7 Desulfurization Crude Carbon Dioxide 8 Hydrocracking Tower 9 Hydrolysis Crude CO ₂ Gas 10 Compressor 11 Dehumidifier 12 Dehumidification Crude CO ₂ gas 13 Deodorization tower 14 Liquefaction raw material CO ₂ gas 15 Liquefaction distillation purification equipment 16 Product liquefaction CO ₂ 17 Off gas 21 Converter furnace gas combustion boiler 22 LDG combustion gas 23 PSA equipment 24 Crude carbon dioxide gas 25 Compressor 26 Deoxygenation tower 27 Hydrogenation Decomposition crude CO ₂ gas 28 Dehumidifier 29 Dehumidification crude CO ₂ gas 30 Deodorization tower 31 Liquefaction raw material CO ₂ gas 32 Liquefaction distillation purification device 33 Product liquefaction CO ₂ 34 Off gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Omori 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Works (72) Inventor Taizo Nakamura 1-20-22 Kita, Chiba City Dojo North (72) ) Inventor Takemitsu Moriyama 3-9-15 Kubo, Kimitsu City, Chiba Prefecture

Claims (1)

[Claims] 1. A carbon dioxide gas contained in a combustion exhaust gas from a boiler or the like is treated by a pressure fluctuation adsorption method to obtain a crude carbon dioxide gas, which is then purified to a high purity carbon dioxide gas by a liquefaction distillation purification device under a compressed state. Prior to this, the crude carbon dioxide gas was pre-compressed to a pressure of 3 to 5 kg / cm ² G, charged into a hydrocracking catalyst packed column, and hydrocracked under conditions of a temperature of 60 ° C. or higher and 100 ° C. or lower. And then pressurized to 15 to 20 kg / cm ² G to remove water and odor, cooled to the saturation temperature of carbon dioxide gas or lower, and supplied to the liquefaction distillation purification device. Raw gas processing method in a refining plant.