JPS6131394B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an air liquefaction separation device that utilizes the cold energy of LNG (liquefied natural gas). The present invention utilizes the cold energy of LNG supplied in large quantities to cool feed air, thereby reducing power consumption. It is an object of the present invention to provide an air liquefaction device that can immediately provide a large amount of cold by heat exchange to a lower rectifying column, and further transfer the cold to an upper rectifying column as quickly as possible. . Hereinafter, one embodiment of the present invention will be described based on the drawings. In Figure 1, 1 is an air filter, 2
is an air compressor, and 3 is an air washing tower. 4 is a so-called reversing heat exchanger, which has 3 parallel heat exchangers.
The flow path 4 is divided into three flow paths 41, 42, and 43.
Raw material air flows back and forth through channels 1 and 42, and refrigerant nitrogen flows through channel 43. 5 is a lower rectification column, 6 is an upper rectification column, 7 is a nitrogen compressor, 8 is an LNG heat exchanger, 9
1 is a flush drum, 10 is a starting valve, 11 is a first switching valve, 12 is a liquid blow valve, 13 is a second switching valve, 1
4 is a raw material air inlet valve, 15a and 15b are liquid air expansion valves, and 15c and 15d are liquid nitrogen expansion valves. Further, a low temperature air discharge valve 16 is provided at the lower part of the upper rectification column 6. That is, as shown in FIG. 2, a condenser 61 is provided in the lower part of the upper rectifying column 6. Above the condenser 61 with a gap 63 is a rectification stage section 6 containing a large number of baffles.
2 is provided. Thus, the discharge valve 16 according to the present invention is provided in the gap 63 so as to open and communicate with the column side wall at a height near the top surface of the condenser 61. The discharge valve 16 has a large diameter of, for example, 6 inches or more. The air liquefaction method will be described above. The raw air is compressed by the air compressor 2 and enters the reversing heat exchanger 4 via the first switching valve 11. Inside the reversing heat exchanger 4, the second
Passing through the switching valves 13a and 13c, passing through the starting valve 10, passing through the second switching valves 13b and 13d, and then passing through the passage 42.
and exits the device via the first switching valve 11. At this time, the liquid blow valve 12, the inlet valve 14, the discharge valve 1
6 is in a closed state, the air flows through the upper rectification column 6.
is in a closed state, the air flows into the upper rectification column 6.
I can't enter. Then, after a certain period of time, the air entering the reversing heat exchanger 4 enters from the passage 42 by the operation of the switching valve 11, and flows through the second switching valve 13b and the first switching valve 13b.
3d, the starting valve 10, and the second switching valve 13.
a and 13c, passes through the passage 41, reaches the first switching valve 11, and similarly flows through the passages 41 and 42 at regular intervals. On the other hand, the circulating refrigerant nitrogen is supplied from the nitrogen compressor 7.
The raw air is passed through the LNG heat exchanger 8 and flash drum 9 to reach the lower rectification column 5, from there it passes through the flow path 43 of the reversing heat exchanger 4, where it is cooled, and then returns to the nitrogen compressor 7 again. In this way, the inside of the apparatus is replaced with nitrogen gas, thereby configuring a nitrogen circulation system. Here, this circulating nitrogen gas becomes low temperature by exchanging heat with LNG, and cools the lower rectification column 5 and the reversing heat exchanger 4. In this way, the amount of LNG and circulating nitrogen gas is increased to gradually advance the cooling of the equipment, but the stage where the cold end of the reversing heat exchanger 4 cools is divided into the following four steps. Manage operations. i.e. -60
If cooling to ℃ is called the first cooling process, cooling to -130℃ is called the second cooling process, cooling to -160℃ is called the third cooling process, and cooling to -172℃ is called the fourth cooling process. 1 At the end of the cooling process, the raw air is
The contained moisture is frozen and adhered to the fins constituting the passage 41 of the reversing heat exchanger, and when it passes through the starting valve 10, most of the moisture is removed, and when it passes through the passage 41,
It recovers the temperature from low temperature to room temperature and exits the device. In the second cooling process, the temperature range is such that CO ₂ contained in the raw air does not precipitate, so the air exhaust valve 16
is opened to the atmosphere, and low-temperature air passing through the starting valve 10 is introduced from the top of the upper rectification column 6 into the column for cooling. In the next third cooling step, since CO ₂ contained in the feed air may be precipitated, the air exhaust valve 16 is closed to stop introducing the feed air to the upper rectification column 6, and the upper rectification is carried out. Cooling of the distillation column 6 is interrupted. Furthermore, in the next fourth cooling step, the raw air contains
CO ₂ precipitates and adheres to the fins of the reversing heat exchanger 4, and when it passes through the startup valve 10, almost all CO ₂
has been removed. Therefore, the air exhaust valve 16
is opened and cooling of the upper rectification column 6 is restarted. Next, the cold end of reversing heat exchanger 4 is -172℃
When this is reached, the inlet valve 14 is opened to admit air into the lower rectification column 5. On the other hand, the nitrogen gas cooled by the LNG heat exchanger 8 is passed through the expansion valve 15d, and the liquid nitrogen generated in the flash drum 9 is passed through the expansion valve 15c.
After that, it is introduced from the upper part of the lower rectification column 5 and rectification is started. Eventually, liquid air accumulates at the bottom of the lower rectification column 5 and the rectification stages. This liquid air is expanded by an expansion valve 15.
After the pressure is reduced in a and 15b, it is supplied to the upper and middle parts of the upper rectifying column 6, and after the rectifying stages of the upper rectifying column 6 are completely cooled, the discharge valve 16 is closed and the Start rectification. At this point, the starting valve 10 is also fully closed. In this way, the product liquefied nitrogen is obtained from the top of the lower rectification column 5, and the product liquefied oxygen is obtained from the bottom of the upper rectification column 6, and these are stored in the liquefied nitrogen tank N and the liquid oxygen tank O, respectively. . Additionally, from the top of the upper rectification column 6, air containing 3 to 4% oxygen, called waste nitrogen, is released, which passes through the second switching valve 13 and exchanges heat with the feed air in the reversing heat exchanger 4. , the temperature is raised to near atmospheric temperature,
It is sent out of the device via the first switching valve 11. In the reversing heat exchanger 4, the waste nitrogen and raw air passages 41 and 42 are alternately switched at regular intervals. An example of operation is described below. The time from the start of cooling until product removal is shown in Table 1.

[Table] Here, A passes through the liquid blow valve 12, B passes through the discharge valve 16, and feeds air into the upper rectifying column 6.
This shows the case when discharged from. In case A, it is difficult for the discharge raw air to flow due to the pressure drop in the liquid blow line, and it takes a long time from the start of cooling to the product extraction, but in case B, the pressure drop is small and a large amount of air is discharged, so Rectification was started in an extremely short time. As described above, in the present invention, in an air separation device that uses the cold energy of LNG for air liquefaction, at the start of operation, the upper rectifying column is cooled in four steps based on the cold end temperature of the air heat exchanger. In the second and fourth steps, a large amount of low-temperature raw material air was introduced into the upper rectification column and discharged into the atmosphere from a discharge valve provided at the bottom of the upper rectification column. As described above, it is effective to provide the discharge valve according to the present invention in an air separation device that can generate the same amount of cold in a short time by using the cold heat of LNG. Therefore, the time from the start of operation until the product liquefied nitrogen and oxygen are produced is significantly shortened.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing one embodiment of the present invention, Figure 2 is a system diagram showing an embodiment of the present invention.
The figure is an enlarged longitudinal sectional view of the main part of the upper rectification column. 2...Air compressor, 4...Reversing heat exchanger, 5...Lower rectification column, 6...Upper rectification column, 7...
...Nitrogen compressor, 8...LNG heat exchanger, 9...Flash drum, 10...Start valve, 11...1st
Switching valve, 12... Liquid blow valve, 13... Second switching valve, 14... Raw material air inlet valve, 16... Raw material air discharge valve.

Claims (1)

[Claims] 1 Compress the nitrogen in the circulating refrigerant nitrogen system using a nitrogen compressor, and use the cold energy through an LNG heat exchanger.
Cooled by LNG, then adiabatically expanded to partially liquefy, introduced into the lower rectification column to cool the feed air, then extracted from the column and passed through an air heat exchanger, where the feed air Chilling is applied by creating a cycle in which air is pre-cooled and then returned to the nitrogen compressor again, and raw air is compressed by the air compressor and passed through the air heat exchanger to pre-cool it, and is then returned to the nitrogen compressor. It is introduced into a rectifying column and cooled, and further introduced into an upper rectifying column to be rectified, and a liquefied nitrogen product is taken out from the lower rectifying column, and a liquefied oxygen product is taken out from the upper rectifying column. In the air liquefaction separation apparatus, a large-diameter discharge valve is installed at the bottom of the upper rectification column to allow a large amount of air cooled by the air heat exchanger and introduced into the upper part of the upper rectification column to pass to the lower part of the column. An air liquefaction separation device characterized by being installed in.