JPH04225778A - Method and device for manufacturing superhigh purity methane - Google Patents

Abstract

PURPOSE:To reduce the cost of superhigh purity methane by a method wherein a liquid of high boiling point component is distillated by a first distillating device, the liquid is used for cooling a capacitor, and superhigh purity methane in a liquid state is recovered from the bottom of a second distillating device to receive fluid taken out from the first distillating device. CONSTITUTION:Liquefied natural gas is introduced to the lower part of a first distillating tower 10, where the gas is distillated and treated. In this case, the mixture liquid of methane and hydrocarbon having a boiling point higher than that of the methane is distillated to the bottom part of the first distillating tower 10. The liquid is first introduced to a capacitor 12 of a tenth distillating tower 10 while a pressure and temperature through a capacitor cooling passage 30. A part of the liquid is vaporized at the tenth distillating tower and the capacitor 12 is cooled by means of a vaporizing latent heat. This method liquefies a part of gas in the top part of the first distillating tower 10 and returns it as reflux to the tower. Remaining fluid (mixture fluid of nitrogen and methane) is introduced to a conveying passage 32, a part of the fluid is introduced to a liquefier 37 for liquefaction, and the liquefied fluid is stored as high purity methane in a product storage tank.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for producing ultra-high purity methane from liquefied natural gas.

0002

BACKGROUND OF THE INVENTION Conventionally, progress has been made in the development of a method for separating and concentrating ultra-high purity methane with a purity of 99.9999% or more from liquefied natural gas as a raw material.

FIGS. 2 and 3 show an example of a conventional ultra-high purity methane production apparatus. All of these devices separate high-purity methane from liquefied natural gas, which contains methane, components with lower boiling points than this methane (mainly nitrogen), and hydrocarbons with higher boiling points than methane (mainly ethane). is configured to do so.

Specifically, in FIG. 2, 90 is a first distillation column for separating low boiling point components such as nitrogen;
A condenser 91 and a reboiler 92 are arranged in the distillation column 90. The liquefied natural gas is first distilled into this first distillation column 90.
is introduced into the middle stage and distilled. A mixed gas of methane and low-boiling components such as nitrogen is discharged from the top of the column, and a mixed liquid of methane and hydrocarbons with a boiling point higher than methane is distilled from the bottom of the column. This mixed liquid is introduced into the bottom of an adsorption tower 93 for separating high boiling point components, and from the top of this adsorption tower 93,
Ultra-high purity methane is emitted in gaseous form. After this gas is liquefied in a liquefier 99, it is collected in a product storage tank.

On the other hand, the apparatus shown in FIG. 3 is similar to the above apparatus until low-boiling components such as nitrogen are separated in the first distillation column 90, but the liquid distilled from the first distillation column 90 is The methane is introduced into a second distillation column 94 for separating high-boiling components, which is equipped with a condenser 95 and a reboiler 96, and ultra-high purity methane is also recovered in gaseous form from the top of this distillation column 94. Further, in this apparatus, a liquid level controller 97 for the first distillation column 90 and a liquid level controller 97 for the first distillation column 90 are provided.
A flow rate controller 9 is installed in the passage (piping) extending from the second distillation column 94 to the second distillation column 94.
8 is arranged, and this flow rate controller 98 adjusts the flow rate of the liquid from the first distillation column 90 to the second distillation column 94 to a constant level, and also controls the flow rate of the liquid in the first distillation column 90 at this flow rate. The liquid level controller 97 adjusts the amount of discharged liquid so as to maintain the liquid level at a predetermined level.

[0006]

Since the operating temperature of the distillation column in each of the above apparatuses reaches approximately -150 DEG C., special means such as liquid nitrogen must be used as a refrigerant source for the condensers 91 and 95. The consumption of such refrigerants greatly affects the cost of ultra-high purity methane.
Reducing this has become a major issue. In addition, these devices recover ultra-high purity methane in a gaseous state.
A refrigerant and a liquefier 99 are required to liquefy and recover this, which is also a major hindrance to cost reduction.

Furthermore, since the adsorption method is used in the apparatus shown in FIG. 2, a regeneration process of the adsorption tower 93 is necessary, and due to this relationship, when batch operation is performed, the production efficiency is poor;
Further, when continuous operation is performed using a plurality of adsorption towers, there is a drawback that an expensive passage switching system is required.

Furthermore, in the apparatus shown in FIG. 3, the flow rate of the liquid transferred from the first distillation column 90 to the second distillation column 94 is kept constant;
In addition, in this state, a part of the liquid must be discharged in order to keep the liquid level in the first distillation column 90 constant, resulting in a corresponding loss in methane recovery.

[0009] In view of the above circumstances, it is an object of the present invention to provide a manufacturing method and apparatus that can efficiently recover ultra-high purity methane and can significantly reduce its cost.

0010

[Means for Solving the Problems] The present invention provides a method for producing ultra-high purity methane from liquefied natural gas, comprising: a first distillation device for separating high-boiling components, which is equipped with a condenser and a reboiler; A mixed fluid consisting of methane and a component with a lower boiling point than methane is taken out from the top of the first distillation device and put into a second distillation device for separating low-boiling components equipped with a condenser and a reboiler. This is a method in which the liquid at the bottom of the apparatus is recovered as ultra-high purity methane, and the bottom liquid of the first distillation apparatus is passed through a condenser of at least one distillation apparatus and evaporated in this condenser (Claim 1).

Furthermore, in this method, better effects can be obtained by recovering a part of the mixed fluid taken out from the top of the first distillation apparatus as high-purity methane, which is lower in purity than the ultra-high-purity methane. (Claim 2).

[0012] As an apparatus for carrying out the above method,
A device for producing ultra-high purity methane from liquefied natural gas, comprising a first distillation device for separating high-boiling components into which liquefied natural gas is introduced, and a condenser and reboiler. , a second distillation device for separating low-boiling components from which the bottom liquid is taken out as ultra-high purity methane; and a second distillation device for extracting a mixed fluid of nitrogen and methane from the top of the first distillation device and sending it to the second distillation device. A transfer passage and a condenser cooling passage for passing the liquid at the bottom of the first distillation apparatus to a condenser of at least one distillation apparatus and evaporating it in the condenser (Claim 3), more preferably, the above-mentioned It is preferable to have a recovery passage branching from the transfer passage and recovering a part of the mixed fluid as high-purity methane having a purity lower than that of the ultra-high purity methane (claim 4).

[0013]

According to the above structure, the liquid distilled from the bottom of the first distillation apparatus is sent to the condenser and evaporated, thereby cooling the condenser with its latent heat of vaporization. That is, the distillate from the first distillation device contributes to cooling the condenser, and the amount of refrigerant used is reduced accordingly. Furthermore, since the ultra-high purity methane is recovered in liquid form from the bottom of the second distillation apparatus, subsequent liquefaction treatment is not necessary.

[0014] Furthermore, in this method and apparatus, the first
By recovering high-purity methane from the top of the distillation apparatus, it is possible to simultaneously obtain ultra-high-purity methane and high-purity methane having different purities.

[0015]

Embodiment FIG. 1 shows an apparatus for producing ultra-high purity methane in one embodiment of the present invention.

This apparatus includes a first distillation column 10 whose purpose is to separate hydrocarbons (mainly nitrogen) with a higher boiling point than methane from liquefied natural gas, and a component (mainly nitrogen) with a lower boiling point than methane.
The second distillation column 20 whose purpose is to separate nitrogen (mainly nitrogen)
Condensers 12 and 22 are arranged in the upper part of each column, and reboilers 14 and 24 are arranged in the lower part, respectively.

A condenser cooling passage (piping in this case) 30 is led out from the bottom of the first distillation column 10, and this condenser cooling passage 30 is connected to the condenser 12 of the first distillation column 10.
, and further passes through the condenser 22 of the second distillation column 20. Further, the top of the first distillation column 10 and the middle part of the second distillation column 20 are communicated via a transfer passage 32, and a recovery passage 34 for recovering high-purity methane is connected from the middle of the transfer passage 32. It is provided. This recovery passage 34 communicates with a product storage tank via a liquefier 37. Further, a recovery passage 38 leading to a product storage tank is led out from the bottom of the second distillation column 20.

Next, a method for producing ultra-high purity methane carried out by this apparatus will be explained.

First, liquefied natural gas, which is a raw material, is introduced into the lower part of the first distillation column 10, where it is subjected to distillation treatment. Specifically, a mixed liquid of methane and a hydrocarbon having a boiling point higher than methane is distilled at the bottom of the first distillation column 10, and this liquid is first distilled into the first distillation column while being reduced in pressure and temperature through the condenser cooling passage 30. It is introduced into the condenser 12 of the distillation column 10, where it partially evaporates, and the condenser 12 is cooled by its latent heat of vaporization. Furthermore, the remaining liquid is introduced into the condenser 22 of the second distillation column 20, where it is evaporated to cool the condenser 22 as well.

By cooling the condenser 12 in this manner, the gas at the top of the first distillation column 10 is partially liquefied and returned to the column as a reflux liquid, and the remaining fluid (a mixture of nitrogen etc. and methane) is liquefied and returned to the column as a reflux liquid. fluid) is led into the transfer passage 32. A part of this fluid is introduced into the liquefier 37 through the recovery passage 34, where it is liquefied and then high-purity methane (concentration 99
．． 9% or more methane) in product storage tanks.

The remaining fluid is introduced into the second distillation column 20, where a distillation operation is performed. Specifically, ultra-high purity methane with a concentration of 99.9999% or more is distilled out as a liquid at the bottom of the column, and this is recovered into the product storage tank through the recovery passage 38, while separated nitrogen, etc. are released from the top of the column. of low-boiling component gases are discharged.

As described above, in this method and apparatus, the first distillation column 10 first distills the high boiling point component liquid, and this liquid is used to cool the condensers 12 and 22. , 22 can be significantly reduced, and more preferably, the refrigerant can be omitted altogether. Then, the fluid taken out from the top of the first distillation column 10 is transferred to the second distillation column 20.
Since the ultra-high purity methane is recovered in liquid form from the bottom of the tank, there is no need to liquefy it during recovery, and costs are further reduced by omitting the liquefaction means and refrigerant required for this process.

[0023] Furthermore, in this apparatus, a part of the fluid distilled from the first distillation column 10 can be recovered as high-purity methane, which is lower in purity than the ultra-high-purity methane. Two types of methane with different values, ie, high-purity methane and ultra-high-purity methane, can be obtained at the same time. Moreover, the production adjustment is also easy.

Table 1 below shows the fluid pressure, temperature, and composition at each point (1) to (2) shown in FIG. This table clearly shows that high purity methane and even higher purity ultra-high purity methane can be obtained at the same time using the above device.

[0025]

[Table 1]

[0026] The present invention is not limited to such an embodiment, and the following embodiments can also be adopted as examples.

(1) In the apparatus of the above embodiment, the condenser 12 in the first distillation column 10 is used as a total condenser and the fluid supplied to the second distillation column is made into a liquid, so that the condenser 22 in the second distillation column 20 is It is possible to further reduce the condensation load. Furthermore, in this case, the collection passage 3
Since the high-purity methane recovered from 4 is also in liquid form, the liquefier 37 and liquid nitrogen as a refrigerant source necessary for liquefaction can be omitted. However, in this case, if the amount of the mixed liquid flowing through the condenser cooling passage 30 is increased in order to completely condense it in the condenser 12, the methane recovery rate will decrease accordingly, so the cost due to this methane recovery rate and the omission of the liquid nitrogen, etc. It is necessary to consider the balance with the reduction of

(2) In the above embodiment, the first distillation column 1
Although a device is shown in which the bottom liquid of 0 is passed through both condensers 12 and 22, the present invention is not limited to this, and the present invention is not limited to this. Even if it is cooled by cooling, the cost can be reduced compared to the conventional method.

[0029]

Effects of the Invention As described above, the present invention first distills a liquid with high boiling point components in the first distillation apparatus, and this liquid is used for cooling the condenser. It is also possible to significantly reduce the amount of refrigerant, and even more preferably to omit the refrigerant altogether. Then, the fluid taken out from the first distillation device is transferred to the second distillation device, and ultra-high purity methane is recovered in liquid form from the bottom of the second distillation device, so it is liquefied during recovery. This eliminates the step of liquefaction, and by omitting the liquefaction means and refrigerant required for this, there is an effect that costs can be further reduced.

[0030] Furthermore, it is possible to recover a part of the fluid distilled from the first distillation apparatus as high-purity methane, which is lower in purity than the ultra-high-purity methane. Two types of methane can be obtained at the same time, and the production can be easily adjusted.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an apparatus for producing ultra-high purity methane in an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing an example of a conventional ultra-high purity methane production apparatus.

FIG. 3 is an overall configuration diagram showing an example of a conventional ultra-high purity methane production apparatus.

[Explanation of symbols]

10 First distillation column (first distillation device) 12, 22 Capacitor 14, 24 Reboiler 20 Second distillation column (second distillation device) 30 Condenser cooling passage 32 Transfer passage 34 Collection passage 38 Collection passage

Claims (4)

[Claims] 1. A method for producing ultra-high purity methane from liquefied natural gas, comprising: introducing the liquefied natural gas into a first distillation device for separating high-boiling components, which is equipped with a condenser and a reboiler; A mixed fluid consisting of methane and components with a lower boiling point than methane is taken out from the top of the methane and put into a second distillation device for separating low-boiling components equipped with a condenser and a reboiler. A method for producing ultra-high purity methane, characterized in that the bottom liquid of the first distillation apparatus is passed through a condenser of at least one of the distillation apparatuses and evaporated in the condenser, while recovering the ultra-high purity methane. 2. The method for producing ultra-high purity methane according to claim 1, wherein a part of the mixed fluid taken out from the top of the first distillation apparatus is recovered as high-purity methane having a purity lower than that of the ultra-high purity methane. 2. The method for producing ultra-high purity methane according to claim 1. 3. An apparatus for producing ultra-high purity methane from liquefied natural gas, comprising a first distillation apparatus for separating high-boiling components, which is equipped with a condenser and a reboiler, into which liquefied natural gas is introduced; Equipped with a capacitor and reboiler,
a second distillation device for separating low-boiling components from which the bottom liquid is taken out as ultra-high purity methane; and a transfer passageway for taking out a mixed fluid of nitrogen and methane from the top of the first distillation device and sending it to the second distillation device. and a condenser cooling passage for passing the liquid at the bottom of the first distillation device through a condenser of at least one distillation device and evaporating it in the condenser. 4. The method for producing ultra-high purity methane according to claim 3, for branching from the transfer passage and recovering a part of the mixed fluid as high-purity methane having a purity lower than that of the ultra-high purity methane. An apparatus for producing ultra-high purity methane, characterized by being equipped with a recovery passage.