JPS5973415A - Preparation of liquefied carbonic acid from waste combustion gas of liquefied natural gas - Google Patents

Abstract

PURPOSE:To prepare liquefied carbonic acid inexpensively and to attempt the control of a total amount of carbon dioxide gas discharged from combustion facilities, by compressing carbon dioxide gas which is separated and collected from a combustion gas of a liquefied natural gas with an absorbent, followed by cooling and condensing it. CONSTITUTION:A combustion gas of a liquefied natural gas is sucked through the channel 3 for treating carbon dioxide gas branched from the flue 1 to the blower 4, cooled to normal temperature by the cooler 5, and sent to the absorbing column 6. It is sprayed with the absorbent 7 such as a carbonate solution, etc. from the top, carbon dioxide is absorbed and sent to the releasing column 9. The separated nitrogen gas, etc. are discharged from the discharge channel 8 through the flue 1 to the stack 2. Carbon dioxide is released from the absorbent 7 by heating the releasing column 9, and the absorbent is recycled through the recycling channel 10 to the absorbing column 6. Carbon dioxide is dehydrated by the dryer 11 packed with a desiccant such as cilica gel, etc., pressurized and compressed to a given pressure by the compressor 12, and cooled and condensed with liquefied natural gas, liquefied carbonic acid, etc. in a low-temperature state by the cooler 13, to give the liquefied carbonic acid 14.

Description

Detailed Description of the Invention The present invention relates to a method for producing liquefied carbon dioxide from the combustion exhaust gas of liquefied natural gas (hereinafter referred to as LNGJ), and in particular, it involves separating and absorbing only carbon dioxide from the LNG combustion exhaust gas and compressing it. The present invention relates to a method for producing liquefied carbonic acid.

Generally, to produce liquefied carbon dioxide (liquefied carbon dioxide) on an industrial scale, carbon dioxide released by igniting limestone or carbon dioxide obtained during the decomposition or reaction process of chemical substances is compressed. It is produced by cooling and condensing carbon dioxide with a refrigerant.

Nowadays, as the consumption of fossil fuels increases due to industrial development, the amount of carbon dioxide released in exhaust gas tends to increase worldwide, and this is accompanied by abnormal weather caused by the so-called greenhouse effect. etc. tend to occur. Therefore, it is gradually becoming desirable to suppress the total amount of carbon dioxide emitted from facilities with large-scale combustion equipment such as thermal power plants, but at present no measures have been taken to reduce carbon dioxide emissions. is not being taught.

In addition, in facilities that have large-scale combustion equipment that uses LNG as fuel, the cold energy of low-temperature LNG is not utilized and is wasted, posing a problem in promoting energy conservation.

The present invention has been devised to effectively solve the above-mentioned problems, and its purpose is to remove only carbon dioxide from LNG combustion exhaust gas that contains few impurities such as sulfur oxides. Liquefied carbon dioxide from LNG combustion exhaust gas can be separated and absorbed and compressed to generate liquefied carbon dioxide, thereby reducing compression energy and suppressing the total amount of carbon dioxide released into the atmosphere. To provide a manufacturing method.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The figure is a process diagram showing an apparatus for producing liquefied carbonic acid for carrying out the method according to the present invention.

In the figure, reference numeral 1 denotes a flue through which exhaust gas discharged from a combustion device (not shown) that burns LNG as fuel is transferred to a chimney 2. The reason why LNG is limited to LNG as a fuel is that LNG has a very low sulfur content compared to other fossil fuels such as heavy oil, and therefore generates less sulfur oxides when burned, so it is necessary to install desulfurization equipment. This is because there is no longer a need for it.

A carbon dioxide processing passage 3 is branched from the flue 1, and exhaust gas can be sucked into this passage 3 by a blower 4 provided in the middle of the passage.The temperature of the introduced exhaust gas is as high as approximately 120°C. Because of this, a cooler 5 is provided in this passage 3 so that the exhaust gas can be lowered to room temperature by using cooling water. An absorption tower 6 for selectively absorbing only carbon dioxide from the exhaust gas is provided downstream of the cooler 5. An absorbent 7, such as a carbonate solution, which is sprayed into the tower and the exhaust gas It is designed so that only carbon dioxide can be separated and absorbed by contacting with the carbon dioxide. A discharge passage 8 connected to the flue 1 is provided in the upper part of the absorption tower 6, and carbon dioxide is removed and the exhaust gas including impurity gases such as nitrogen gas is returned to the flue 1. It is now possible to introduce it into The absorbent used in this absorption tower 6 may be either wet or dry.

A release group 9 is provided on the downstream side of the absorption tower 6 to release carbon dioxide as a gas from the absorbent that has absorbed carbon dioxide in the absorption tower 6. By applying heat, for example, to the absorbent, it is possible to release carbon dioxide and regenerate the absorbent. The regenerated absorbent here can be reintroduced into the absorption tower 6 via the releasing group 9 and an absorbent recycling passage 1o connected to the absorption tower 6.

A dryer 11 filled with a desiccant such as silica gel is installed further downstream of the release group 9, and dries the carbon dioxide released by the release group 9 to a few ppm of moisture. I'm starting to get it. Note that if carbon dioxide is to be absorbed by a dry absorbent in the absorption tower 6, the dryer 11
It is also possible to have a small-capacity one, or to omit it.

A compressor 1 is installed downstream of this dryer 11.
2 is provided so that the carbon dioxide dried by the dryer 11 can be pressurized to a predetermined atmospheric pressure or higher.

This compressor 12 compresses only substantially pure carbon dioxide that is not mixed with nitrogen gas or the like.

A carbon dioxide liquefaction cooler 13 that uses low-temperature LNG or liquefied carbonic acid as a refrigerant is provided further downstream of the compressor 12.

The carbon dioxide compressed by the compressor 12 is cooled and condensed using cold heat such as low-temperature LNG (approximately -160'G) to liquefy it and finally obtain liquefied carbon dioxide.

Note that the boiling point of carbon dioxide is approximately -50°C and approximately 5 atmospheres. Further, a rectification column may be provided downstream of the cooler 13 to purify the liquefied carbonic acid produced here.

Next, a method according to the present invention using the liquefied carbonic acid production apparatus configured as described above will be explained.

First, exhaust gas generated by burning LNG in a combustion device (not shown) flows through a flue 1 toward a chimney 2 . Since LNG, the fuel, contains almost no sulfur, this exhaust gas contains almost no sulfur oxides, and the carbon dioxide content is between 2.5 and 9.
v01%, and in normal atmosphere (0.03vo1
%).

A part of the exhaust gas flowing in the flue is sucked into the carbon dioxide processing passage 3 from the flue 1 by the blower 4, and since the temperature of this exhaust gas is as high as approximately 120°C, it is first passed through the cooler 5 using cooling water as a refrigerant. and cooled to room temperature. At this time, water vapor contained in the exhaust gas is cooled and condensed, and a large amount of distilled water W is discharged. The cooled exhaust gas is further transferred and introduced into the absorption tower 6 located on the downstream side.
Carbon dioxide is separated and absorbed from the exhaust gas by contact with the absorbent (liquid) that is being circulated within the tower. Impurity gas such as nitrogen remaining without being absorbed here is discharged and disposed of through the exhaust passage 8 to the flue 1, and in this way, the impurity gas and carbon dioxide are separated.

After the absorbent that has absorbed carbon dioxide is discharged from the absorption tower 6, it is then introduced into the release group 9, where it is subjected to heat treatment, for example, to release the carbon dioxide absorbed in the absorption tower, and the carbon dioxide absorbed in the absorption tower is released. Pure carbon dioxide can be obtained.

The absorbent regenerated within the release group 9 is transferred to the absorption tower 6 via the absorbent recycling passage 10 and is reused.

The nearly pure carbon dioxide that has been collected is then introduced into the dryer 11, where it is reliably dried by a desiccant such as silica gel filled therein, and the moisture contained therein is removed. . The reason for drying in this way is to prevent the formation of ice when cooling to a low temperature in the later stage.

The carbon dioxide dried in the dryer 11 is then introduced into the compressor 12 on the downstream side and compressed to several atmospheric pressures. Of course, the pressure applied here is set to a pressure value or higher that can liquefy even if volumetric contraction occurs due to cooling in the latter stage. In particular, this compressor 12 compresses only substantially pure carbon dioxide that is not mixed with impure nitrogen gas, so it is more efficient than conventional compressors that include impurity gases. The cost of driving the compressor can be reduced.

Here, the pressurized carbon dioxide is further introduced into the carbon dioxide liquefaction cooler 13 on the downstream side, where it is cooled by the cold heat of low-temperature LNG (approximately -160°C) used as a refrigerant. is cooled and liquefied, and finally liquefied carbonic acid 14
will be generated.

Although the compressor 12 is provided downstream of the dryer 11 in the above device example, it may be provided in the opposite direction.

LNG is a fuel with almost no sulfur content.
Since we decided to burn it and capture carbon dioxide from the combustion exhaust gas, there is no need to install attached equipment such as desulfurization equipment, and it is possible to suppress the total amount of carbon dioxide released into the atmosphere. .

In addition, only carbon dioxide is separated and collected by the absorption tower 6 and the release group 9, and only the collected substantially pure carbon dioxide is compressed by the compressor 12, so that nitrogen gas, etc. Compared to compressing a mixture of impurity gases, the operating cost of the compressor can be reduced by 1.
] can be reduced to

Furthermore, as the refrigerant used in the carbon dioxide liquefaction cooler 213, low-temperature LNG, which is a fuel for combustion equipment, can be used, so there is no need to use a special refrigerant, which is economical.

In summary, according to the present invention, the following excellent effects can be achieved.

(1) Since we decided to burn liquefied natural gas as a fuel that contains almost no sulfur content and separate and collect carbon dioxide from the resulting exhaust gas, it is necessary to install attached equipment such as a desulfurization device. There is no.

(2) Since we decided to compress only the captured carbon dioxide to generate liquefied carbon dioxide, the compressor drive is much faster than when compressing a mixture of impurity gases such as nitrogen gas, as in the conventional case. Costs can be drastically reduced.

(3) Since the amount of carbon dioxide released into the atmosphere can be suppressed, the occurrence of pollution caused by carbon dioxide can be prevented.

(4) Since low-temperature liquefied natural gas, which is a fuel, can be used as a refrigerant to cool and liquefy compressed carbon dioxide, it is possible to eliminate the need for energy for supplying cold heat.

[Brief explanation of the drawing]

The figure is a process diagram showing an apparatus for producing liquefied carbonic acid for carrying out the method according to the present invention. In the figure, 1 is a flue, 3 is a carbon dioxide processing passage, 6 is an absorption tower, 7 is an absorbent, 9 is a release group, 12 is a compressor,
13 is a carbon dioxide liquefaction cooler, and 14 is a liquefied carbon dioxide. Patent Applicant: Nobuo Kinutani, Patent Attorney, Ishikawajima-Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] The combustion exhaust gas of liquefied natural gas is brought into contact with an absorbent to separate and absorb carbon dioxide from the exhaust gas, the absorbed carbon dioxide is released and collected, and the collected carbon dioxide is then compressed. A method for producing liquefied carbonic acid from combustion exhaust gas of liquefied natural gas, characterized in that the liquefied carbonic acid is cooled to produce liquefied carbonic acid.