JPS5973416A - Preparation of liquefied carbonic acid from waste combustion gas of liquefied natural gas - Google Patents

Abstract

PURPOSE:To prepare liquefied carbonic acid by simple facilities, to produce water as a by-product, and to suppress a release amount of carbon dioxide gas into atmosphere, by compressing a waste combustion gas of liquefied natural gas, drying, and cooling it so that carbon dioxide is liquefied. CONSTITUTION:A liquefied natural gas is burned to produce a waste gas in an unsaturated steam state containing almost no sulfur, which is sucked from the flue 1 by the blower 4, introduced into the humidifying and dehumidifying column 5. First, it is brought into contact with the spraying sea water a at the dehumidifying part 5a, cooled and changed into a saturated steam state, it is then subjected to indirect heat exchange at the dehumidifying part 5b with the pure water b previously cooled with the sea water a, it is further cooled to give the condensed pure water c. The waste water is then cooled with a refrigerant by the cooler 6 to about 3-10 deg.C, to give the condensed pure water d. The waste gas in an unsaturated steam state is pressurized by the compressor 7 into a given pressure, passed through the dryer 8 packed with a desiccant, cooled further with a low-temperature liquefied natural gas by the cooler 10, the liquefied carbonic acid 11 is taken out, and the remaining gas e is discharged to the flue 1.

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, a method for producing liquefied carbon dioxide from the exhaust gas generated by burning LNG. This invention relates to a novel 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 manufactured by cooling and condensing compressed carbon dioxide using a refrigerant.

At present, as the consumption of fossil fuels increases due to industrial development, the amount of carbon dioxide contained in exhaust gas and released is increasing worldwide, and this is accompanied by abnormal weather conditions caused by the so-called greenhouse effect. tends to be caused. Therefore, it is gradually becoming desirable to reduce the total amount of carbon dioxide emitted from facilities with large-scale combustion equipment such as thermal power plants, but at present there is no effort to reduce the amount of carbon dioxide emissions. No measures have been taken. Furthermore, in facilities with large-scale combustion equipment that use LNG as fuel, the cold energy of low-temperature LNG is not utilized and is wasted, posing a problem in promoting energy conservation.

In view of the above-mentioned problems, the present invention was devised to effectively solve the problems, and its purpose is to extract fresh water from the unsaturated steam exhaust gas generated by burning LNG. An object of the present invention is to provide a novel method for producing liquefied carbonic acid, which recovers liquefied carbonic acid and produces liquefied carbonic acid.

Hereinafter, a preferred embodiment 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 requires desulfurization equipment, etc. This is because there is no need to provide it.

A carbon dioxide processing passage 3 is branched from the flue 1, and a blower 4 provided in the middle of the passage
It is designed to allow exhaust gas to be sucked into the tank. This introduced exhaust gas has a high temperature of approximately 120°C and contains a large amount of moisture, so in order to lower this temperature and recover the moisture, a humidification and temperature reduction tower is installed in the passage 3. 5 is provided. Specifically, the humidification/temperature reduction tower 5 is a tower in which the cylinder body is filled with two layers of packing material, and the lower layer inside contains seawater a in the exhaust gas introduced into the tower.
Humidifying parts 5a-jf are formed by spraying the water to increase the humidity and bring it into a saturated steam state, and the upper layer of the humidifying part 5a is filled with fresh water pre-cooled by the seawater a. A dehumidification section 5b is formed for generating condensed water (fresh water) C while lowering the temperature of the exhaust gas to around 40° C. by exchanging heat with the exhaust gas. In addition, the generated and recovered fresh water C
The majority of this will be re-cooled and circulated as a refrigerant to lower the exhaust gas temperature. This condensed water becomes manufactured water (fresh water), that is, the humidification and temperature reduction tower performs the function of desalinating seawater.

A cooler 26 is provided downstream of the humidification/temperature reduction tower 5 to further cool the exhaust gas transferred through this tower, and cools the temperature of the introduced exhaust gas to around 3 to 10°C. Along with this cooling, a large amount of condensed water (fresh water) d can be recovered. A compressor 7 is provided on the downstream side of the cooler 6, so that the exhaust gas, which has been made into a cine-saturated steam state by removing a large amount of condensed water in the cooler 6, can be pressurized to a predetermined pressure or higher. It has become.

Furthermore, a dryer 8 filled with a desiccant such as silica gel is provided downstream of the compressor 7, and is capable of drying the introduced exhaust gas to a water content of several ppm. By interposing a cooler 9 between this dryer 8 and the compressor 7 as shown by the imaginary line, the temperature of the exhaust gas introduced into the dryer 8 is lowered, and the moisture contained therein is further condensed and removed. In this way, the capacity of the dryer 8 can be reduced in size.

A carbon dioxide liquefaction cooler 10 that uses low-temperature LNG as a refrigerant is installed downstream of this dryer 8, and converts the exhaust gas compressed by the compressor 7 into low-temperature LNG (approximately 2160°C). Cooled by cold heat,
Only the carbon dioxide contained in the exhaust gas is liquefied, and liquefied carbonic acid 11 is finally obtained. This exhaust gas contains various gases such as nitrogen and oxygen in addition to carbon dioxide, but the boiling point of carbon dioxide is approximately -50°C and approximately 5 atm, and it can be liquefied more easily than other gases. Can be done. Therefore, any remaining gas e that is not liquefied in the liquefaction cooler 10 is returned to the flue 1 and treated as waste gas.

In the above device example, the exhaust gas is introduced into the compressor 7 via the humidification and temperature reduction tower 5 and the cooler 6. It may also be introduced into the compressor 7. In this case, since the exhaust gas contains a large amount of water, a cooler 9 shown in the imaginary line is installed downstream of the compressor 7 to cool the exhaust gas and convert it into condensed water (fresh water).
f is collected.

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

First, exhaust gas generated by burning LNG in a combustion device (not shown) flows through a flue 1 toward a chimney 2 . LNG, the fuel, contains almost no sulfur and has a carbon dioxide content of 2.5 to 9 vo.
1% in normal atmosphere (0.03vo1%)
The concentration is much higher.

A part of the exhaust gas flowing in the flue is sucked into the carbon dioxide processing passage 3 by the blower 4, and is introduced into the humidifying section 5B in the humidifying and temperature reducing tower 5 as it is. Since this exhaust gas has a high temperature of 130'C and is in an unsaturated steam state, it is brought into contact with the seawater a sprayed in the humidifying section 5a, and the seawater is blown away. It evaporates and becomes a saturated water vapor state. Note that this seawater will be directly discharged outside the tower. The exhaust gas, which has been cooled to approximately 5o to 70'C and has reached a saturated steam state, rises as it is and is then introduced into the dehumidification section 5b. This exhaust gas undergoes indirect heat exchange with fresh water pre-cooled by the seawater a, and the exhaust gas temperature is lowered to around 38 to 50°C, and a large amount of condensed water (clean water) C is generated accordingly. It will be collected. Most of this recovered fresh water C is returned to seawater a! It is incinerated and used as a refrigerant to lower the exhaust gas temperature, but a portion of it is transferred to other systems.

The exhaust gas discharged from the humidification/temperature reduction tower 5 is transferred further downstream and introduced into the cooler 6 while maintaining a saturated steam state. This exhaust gas is cooled to about 3 to 10° C. by the refrigerant in the cooler 6, and as a result, a larger amount of condensed water (fresh water) d is generated and recovered. The amount of fresh water recovered here is comparable to the amount of fresh water obtained in the humidification and temperature reduction tower 5, and this large amount of fresh water is used as boiler water in power plants, for example.

The exhaust gas is cooled in the cooler 6 and most of the moisture contained therein is removed, becoming an unsaturated steam state and introduced into the compressor 7 provided further downstream, where it is pressurized to a predetermined pressure or higher. will be done.

At this time, most of the water contained in the pressurized exhaust gas is removed and it is in an unsaturated steam state, so even if it is pressurized and compressed, no water is generated as condensation.

Then, the pressurized exhaust gas is introduced into the dryer 8 installed on the downstream side, where it is dried by a drying agent such as silica gel filled in it, and the water contained in it is dried. will definitely be removed. The purpose of this drying is to prevent the formation of ice when the exhaust gas is cooled in the latter stage.

The dried exhaust gas is further introduced into the carbon dioxide liquefaction cooler 1o provided on the downstream side, where it is cooled by the cold heat of low-temperature LNG (approximately -160°C) used as a refrigerant. Thereby, only the carbon dioxide contained in the exhaust gas can be liquefied, and liquefied carbonic acid 11 can be finally generated.

Here, this exhaust gas contains nitrogen in addition to carbon dioxide.

It contains various gases such as oxygen, but the boiling point of carbon dioxide is approximately -50'C1, approximately 5 atmospheres, and other gases can be easily liquefied. Therefore, the gas e other than carbon dioxide, such as nitrogen, which remains without being liquefied in the cooler 10 is returned to the flue 1 and released into the atmosphere. Furthermore, the low-temperature LNG used as a refrigerant in this cooler 10 is used as fuel for combustion equipment (not shown) that is an exhaust gas source, and there is no need to drive a compressor or the like to generate cold heat. .

In this way, we decided to burn liquefied natural gas as a fuel that contains almost no sulfur, and liquefy only carbon dioxide from the resulting exhaust gas to produce liquefied carbonic acid, so there is no sulfur in the exhaust gas. It contains almost no oxides, so there is no need to install attached equipment such as a desulfurization device.

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

(1) Since carbon dioxide is liquefied and recovered from the exhaust gas produced by burning liquefied natural gas as a fuel that contains almost no sulfur content, there is no need to install attached equipment such as a desulfurization device.

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

(3) Since low-temperature liquefied natural gas, which is a fuel, can be used as a refrigerant to cool and liquefy carbon dioxide,
Energy for supplying cold and heat can be eliminated. .

(4) A large amount of fresh water can be recovered as a by-product,
There is no need to newly generate boiler water, etc.

[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, 5 is a humidification/temperature reduction tower, 6 is a cooler, 7 is a compressor, 8 is a dryer, 10 is a carbon dioxide liquefaction cooler, and 11 is liquefied carbonic acid. Patent Applicant: Nobuo Kinutani, Patent Attorney, Ishikawajima-Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] Liquefaction characterized by compressing unsaturated steam exhaust gas obtained by burning liquefied natural gas, drying the compressed exhaust gas, and then cooling it to produce liquefied carbonic acid. A method for producing liquefied carbonic acid from natural gas combustion exhaust gas.