JPH04121573A - Method of liquifying co2 gas - Google Patents

Abstract

PURPOSE:To reduce an energy consumption and recover a power by a method wherein liquid hydro-carbon refrigerant not containing halogen element which is not condensed even at a boiling point of LNG is applied as an intermediate refrigerant, the refrigerant is cooled and liquified by evaporation latent heat of LNG and then CO2 gas is liquified by the evaporation latent heat of the intermediate refrigerant. CONSTITUTION:As liquid hydro-carbon refrigerant not containing halogen elements, methane, ethane, propane or the like not condensed even at a boiling point of LNG under an atmospheric pressure are pointed out. Although its boiling point is a sufficient temperature where CO2g becomes CO2l, a temperature of the intermediate refrigerant is increased in such a way as the refrigerant is not condensed into CO2. This intermediate refrigerant is singly applied or mixed with another substance and enclosed in an intermediate refrigerant circulation line 3, thereby a temperature of the intermediate refrigerant heat exchanged with CO2g can be decreased less than a boiling point of fluorocarbon 22 and then an amount of energy required for compressing CO2 gas can be saved. Since evaporated LNGg has a high pressure and a low temperature, this is heated with water through its heat exchanging operation, its temperature is increased up to its normal temperature and then the LNGg is supplied to a turbine and its power can be recovered.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for liquefying CO2 gas, and in particular to a method for liquefying CO2 gas.
This invention relates to a method for liquefying gas.

[Conventional technology]

Conventionally, the cold energy of LNG is used to cool halogenated hydrocarbons (hereinafter abbreviated as fluorocarbons), which are intermediate refrigerants.
A method is known in which CD2 gas is cooled and liquefied using cooled Freon.

Hereinafter, a method of liquefying CO2 gas using Freon as an intermediate refrigerant will be explained with reference to FIG.

In Figure 1, 1.2 is a heat exchanger, 3 is a fluorocarbon circulation line, 4 is a circulation pump, 5 is an LNG (1) supply line, 6 is an LNG (g) discharge line, and 7 is a CO2 (g)
) supply line, 8 is CD□(1) discharge line.

LNG supplied from supply line 5 to heat exchanger 1 <1
The fluorocarbon (g) circulating through the circulation line 3 is cooled by the latent heat of vaporization of the fluorocarbon (g), and the fluorocarbon (g) is liquefied into fluorocarbon <i>. The LNG (1) is evaporated into LNG (g), taken out of the system through the discharge line 6, and supplied to the LNG (g) usage source.

Freon (1) is supplied to the heat exchanger 2 by the circulation pump 4, and C02 (g) supplied from the supply line 7 is converted to CD by the latent heat of vaporization of the Freon (1).

(β) is cooled and liquefied and taken out of the system through the discharge line 8, and at the same time, the fluorocarbon (i) becomes fluorocarbon and (g) and is circulated through the circulation line 3 to the heat exchanger 1 as mentioned above. be done.

When liquefying CD□ (g), since CD2 has a temperature-pressure curve as shown in Figure 3, the recovered CD2 gas generally has to be compressed, but when it is compressed, CO2 ( g) becomes high temperature, this high-temperature, high-pressure CD□ (g) is cooled with air or water, and when it is supplied to the system shown in Figure 1 above, the COC02 (generally has an average temperature of about 40°C). Yes, this 40℃ CD
□When (g) is cooled by an intermediate refrigerant (in this case, Freon) in a normal heat exchanger 2, a temperature difference (generally called approach temperature) is required.
The temperature difference between the intermediate refrigerant temperature and the liquid CD□ was set at 20°C.

In order to liquefy CO2 (g) into CD□ (Il), it is necessary to compress the pressure of CO2 (g) supplied from supply line 7 to a pressure commensurate with the temperature-pressure curve shown in Figure 3. .

At this time, when Freon 22, a typical type of fluorocarbon, is used as the intermediate refrigerant, the boiling point of Freon 22 under atmospheric pressure is -40.8°C, so the temperature of the obtained C0C02 is approximately -20.8°C.
℃, and in order to liquefy CO2 (g), the supply co2
The <g> pressure must be approximately 20.4 ata. For this reason, COC02 under atmospheric pressure (20. d
The energy required to compress it to ata is considerable.

Furthermore, Freon-22 is not subject to regulation. In recent years, there has been a trend toward banning the use of Freon as it is a substance that causes the destruction of the ozone layer in the earth's atmosphere.

[Problem to be solved by the invention]

The present invention has been developed in view of the above-mentioned state of the art, and the present invention has been developed to replace fluorocarbons by using an intermediate refrigerant that does not have the disadvantages of fluorocarbons and can consume less energy than liquefying CO2 gas using fluorocarbons as an intermediate refrigerant. The object of the present invention is to provide a method that can liquefy gas, and also provide a method that can recover the pressure energy of LNG (g) obtained by cooling an intermediate refrigerant as power.

[Means to solve the problem]

The present invention (1) uses a halogen-free liquid hydrocarbon refrigerant that does not solidify even at the boiling point of LNG as an intermediate refrigerant;
A method for liquefying CO2 gas by cooling and liquefying the intermediate refrigerant using the latent heat of evaporation of the cooling liquefied intermediate refrigerant, and liquefying the C02 gas without solidifying it using the latent heat of evaporation of the cooled and liquefied intermediate refrigerant.

(2) In the above method, a CD and gas liquefaction method in which power is recovered by rotating a turbine using high-pressure steam of evaporated LNG.

It is.

[Effect]

As a halogen-free liquid hydrocarbon refrigerant that can be used in the present invention, the boiling point of LNG under atmospheric pressure (approximately -
The following table shows that they do not solidify even at 161.5°C), and they can be used alone or in combination.

Specific examples of intermediate refrigerants When using the above-mentioned intermediate refrigerants alone or in combination, the boiling point should be set to [:02 (g) at a temperature sufficient to become 002 (i), but solidify to C02 (s ), it is necessary to raise the temperature of the intermediate refrigerant. CL (g
) The temperature of the intermediate refrigerant supplied to the heat exchanger that exchanges heat with the refrigerant can be lowered by more than ten degrees Celsius than the boiling point (-40.8℃) of conventional Freon 22 (of course, it can be lowered even further). It is possible, but to avoid coagulation,
(No further reduction in boiling point is allowed) The amount of pressurized CL gas supplied to the heat exchanger can be reduced accordingly, and the amount of energy required for CD2 gas compression can be saved.

Furthermore, since the vaporized LNG (Cg) is under high pressure, the gas can be supplied to the turbine to rotate the turbine and recover power, but the vaporized LNG (Cg)
Since the temperature of the gas is too low, it is preferable to heat the gas by heat exchange with water, for example, to raise the gas temperature to about room temperature before supplying the gas to the turbine.

[Example 1] Below is the 11th! ! The effect of the present invention is demonstrated by comparing the case where ethane is used as an intermediate refrigerant as an example of the present invention according to the flow of I and the case where Freon 22, which is a conventional intermediate refrigerant, is used. .

Under the conditions shown in the table above, in the embodiment of the present invention, C02 gas is compressed from 1.03 ata to 12.7 ata (2
Stage compression) is sufficient, so [0□ compressor power is 6210 KW) l/h is sufficient, whereas in the conventional example using Freon 22, C02 gas is 1.03
20. from ata. Since it is necessary to compress (two-stage compression) to d data, C02 of 7330 KIIIH/H
Compressor power is required.

As a result, the embodiment of the present invention achieves a significant power saving compared to the conventional method.

Although the above embodiment shows an example in which ethane is used as the intermediate refrigerant, the present invention is not limited to this, and other intermediate refrigerants shown in Table 1 may be used alone or in a mixture, and the intermediate refrigerant may be used as appropriate. By setting the confinement pressure in the circulation line, corresponding savings in power consumption are possible.

[Example 2] According to the flow shown in FIG. 2, an example of power recovery from LNG gas of the present invention will be shown to prove the effects of the present invention. In FIG. 2, numerals 1 to 8 are the same as in FIG. 1, so their explanation will be omitted. The added numeral 9 in FIG. 2 is a heat exchanger, 1
0 is an expansion turbine.

In FIG. 2, low-temperature LNG (g) discharged from the heat exchanger 1 through the discharge line 6 is transferred to the heat exchanger 9.
After exchanging heat with water, for example, it is supplied to the expansion turbine 10 and power is recovered.

A replica was made under the conditions shown in comparison with Example 1, and the discharge line 6
The low-temperature LNG (g) discharged from the
The temperature is raised to 0°C, and the inlet pressure to the expansion turbine 10 is 10ata.
When supplied at a pressure of 4ata and taken out at an outlet pressure of 4ata, the recovery power is 3140 WH/II under the conditions of the embodiment of the present invention.

It can be seen from Example 2 that the method of the present invention can recover power during liquefaction of CD and gas, and is industrially advantageous.

〔Effect of the invention〕

According to the present invention, when liquefying CD gas, the power energy due to CO2 gas compression can be significantly reduced compared to the conventional method, and the power can be recovered, and its industrial value is extremely significant.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the prior art and Embodiment 1 of the present invention, FIG. 2 is an explanatory diagram of Embodiment 2 of the present invention, and FIG. 3 is a temperature-pressure relationship chart of the liquefaction curve of C02 gas.

Claims (2)

[Claims] (1) A halogen-free liquid hydrocarbon refrigerant that does not solidify even at the boiling point of LNG is used as an intermediate refrigerant, and LNG
A method for liquefying CO_2 gas, characterized in that the intermediate refrigerant vapor is cooled and liquefied by the latent heat of evaporation of the cooled liquefied intermediate refrigerant, and the CO_2 gas is liquefied without being solidified by the latent heat of evaporation of the cooled and liquefied intermediate refrigerant. (2) A method for liquefying CO_2 gas according to claim (1), characterized in that power is recovered by rotating a turbine using evaporated high-pressure LNG steam.