JPH0316598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-temperature compression method for feed air in an air separation device, and more specifically, the feed air compression process in an existing air liquefaction separation device is performed using liquefied natural gas (hereinafter abbreviated as LNG). The present invention relates to a method of performing a low-temperature compression process using cold temperatures.

When using LNG for power generation or city gas, etc.
Many attempts have been made to reduce the electricity consumption rate for products such as oxygen and nitrogen by utilizing the refrigeration of LNG for liquefaction and separation of air, and actual equipment is already in operation. However, these conventional methods mainly exchange heat between dry nitrogen in a circulating nitrogen system installed in the equipment and LNG to provide cooling. That is, conventionally, low-temperature compression of circulating nitrogen has been performed, but low-temperature compression of feed air has not been performed. The reason for this is that a method for removing moisture in the raw material air before low-temperature compression has not been elucidated. There is a method of dehydrating raw air by washing it with methanol, but there are problems with safety during compression and safety during washing.Also, there is a method of dehumidifying using a desiccant, but it requires electricity to regenerate this desiccant. I need.

The present invention was developed in view of the above, and utilizes the refrigeration of LNG to cool the raw air temperature of the air liquefaction separation device to approximately -140°C, simultaneously removes the moisture contained therein, and transfers this low-temperature dry air to an air compressor. By performing low-temperature compression using this method, the power unit required for compression is 1/2.3 of that for room-temperature compression, thereby reducing the power unit required for air separation.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the method of the present invention. Temperature of air entering from air intake port 1: 30℃, humidity: 80℃
The air at ℃ is approximately 0.1~0.15 by air blower 2.
It is compressed to kg/cm ² , heated to 38° C., and introduced into the warmer 3. In the warmer 3, this raw material air exchanges heat with the first circulating refrigerant flowing countercurrently, and the first circulating refrigerant enters the flow path _10b2 of the air cooler 10b, which will be described later. It is heated to a temperature at which the moisture deposited in the other flow path _10b1 can be purged, and the temperature is lowered to about 26° C., and the air is led out through the pipe 4 and enters the air precooler 5. In the air precooler 5, heat is exchanged with a dry low-temperature compressor flowing countercurrently, the temperature is lowered to about 2°C, and the air is discharged.Then, the air enters a water separator 6 to separate the condensed water, and is passed through a pipe 7.
It forms a pair through a pipe 8 and a valve 9, and enters a flow path _10a1 of one of the air coolers 10a, which is used selectively. The low-pressure raw material air that has entered the flow path 10a ₁ of the air cooler 10a exchanges heat with the first circulating refrigerant (fluorocarbon or nitrogen) flowing countercurrently through the other flow path 10a ₂ , and its temperature is lowered to -140°C.
At the same time, moisture condensed on the tube wall of the flow path _10a1 is precipitated and turned into low-temperature dry air, which is led to the tube 13 via the tube 11 and the valve 12. The first circulating refrigerant (fluorocarbon or nitrogen) is supplied to the first LNG heat exchanger 14, which will be described later.
The temperature is lowered to -145°C by exchanging heat with LNG, and the temperature is lowered to -145°C by the cooling, and the air is introduced into the air cooler 10a. After cooling the low-pressure raw material air, the air is led out to the first refrigerant circulation pump 15.
After being pressure-fed and heated by the warmer 3, the LNG enters the other air cooler 10b, where it is heated, and then returns to the first LNG heat exchanger 14 for circulation. The low temperature dry air of about -140° C. and about -200 mmAg in the pipe 13 is then introduced into an air compressor 16 consisting of multiple stages. In this example, the final stage discharge pressure is 5Kg/
cm ² and a five-stage compression isothermal compressor.
That is, each stage 16a, 16b, 16c, 16d, 16
Since the temperature of the discharged air in e is raised by about 20°C due to the heat of compression, the compressed dry air discharged from each stage 16a, 16b, 16c, and 16d enters the compressed air cooler 17 and is cooled down to -140°C. It will be compressed again. The compressed air cooler 17 is supplied with cold air from LNG flowing countercurrently in a second LNG heat exchanger 18 to be described later, and a second circulating refrigerant (Freon) is circulated by a second refrigerant circulation pump 19 at -140 °C. It is filled with ℃.
The second LNG heat exchanger 18 has a temperature of -160℃ from the pipe 20.
LNG is introduced and the second circulating refrigerant is heated to -150°C.
It is then cooled down to a temperature of -135°C and then brought out for use. The final stage 16e of the air compressor 16
The compressed dry air discharged at 5 kg/cm ² G and -125° C. is then introduced into the nitrogen heat exchanger 21, where it is heat exchanged with waste nitrogen discharged from the countercurrent air liquefaction separation device 22 and introduced through the pipe 23. The temperature of the waste nitrogen is then lowered from room temperature to -120°C, and the temperature of the waste nitrogen itself is raised to -42°C before being discharged from the pipe 24. The compressed dry air at -42°C then enters the air precooler 5 and exchanges heat with the raw material air flowing countercurrently, lowering its temperature to about 2°C, and the air itself is about 24°C.
The temperature is raised to .degree. C., and the air is drawn out through a pipe 25 and introduced into the air liquefaction separation device 22. Atmospheric air is like this
The LNG is cooled and dehumidified using the cold temperature of the LNG, compressed at a low temperature, and then sent to the existing air liquefaction separation device 22 as compressed raw air.

Next, the low temperature dehumidification process which is a feature of the present invention will be described in more detail with reference to FIGS. 2 and 3. When the air precooler 10a is in the air cooling period, low-pressure raw material air flows from the pipe 8 to the pipe ₁₁ in the flow path 10a1.
Cooled by the _first circulating refrigerant flowing through the flow path 1
When the moisture contained in the pipe wall of 0a ₁ is being condensed and precipitated, the other air cooler 1 in the pair is used in a switching manner.
0b is the regeneration period (Fig. 2), and the flow path 10
The first circulating refrigerant at -1°C from which a ₂ has been derived is pumped by the first refrigerant circulation pump 15 through valves 49 and 50, enters the warmer 3, and is heated to 20°C. Next, the waste nitrogen from the air liquefaction separation device 22 flowing countercurrently through the valve 26 enters the flow path 10b ₂ of the air cooler 10b and is heated up, and the waste nitrogen itself is cooled to about -61° C. and then passed through the pipe 27.
The LNG enters the first LNG heat exchanger 14 through valves 28 and 29 and is cooled down to approximately -145°C, and then flows into the pipe 30.
After passing through the valve 31, the air cooler 1 is discharged again.
It enters the flow path _10a2 of 0a and circulates. LNG at a temperature of -150°C is introduced into the first LNG heat exchanger 14 through a pipe 32, heat-exchanged with the first circulating refrigerant, vaporized, and led out through a pipe 33 at a temperature of -65°C to be supplied to a user. Further, the waste nitrogen from the air liquefaction separation device 22 is discharged from the nitrogen heat exchanger 21 at -120°C, and then passes through the pipe 34 and valve 35 to the flow path 1 of the air cooler 10b in the regeneration period.
_0b1 , and is heated by the first circulating refrigerant flowing counter-currently, evaporates the moisture that had been deposited on the pipe wall in the previous cycle, and brings it out through the pipe 36 at about 15°C, with the valve 37,
It is discharged out of the device via pipe 38. On the contrary, when the air cooler 10a is in the regeneration period and the air cooler 10b is in the air cooling period, the operating state is as follows (3rd
figure). The low-pressure raw material air led out of the water separator 6 passes through a pipe 40 and a valve 41, enters the flow path _10b1 of one of the pair of air coolers 10b, and is cooled by the first circulating refrigerant flowing countercurrently, and its temperature is lowered. At the same time, the contained moisture is condensed and deposited on the pipe wall of the flow path _10b1 to become low-temperature dry air. The low-temperature dry air led out of the flow path 10b ₁ is introduced into the air compressor 16 from the pipe 13 via a pipe 42 and a valve 43. Further, the first circulating refrigerant circulates through the next system. That is, the first circulating refrigerant that has been led out of the first LNG heat exchanger 14 at a lower temperature than the pipe 30 passes through the valve 44, the pipe 45, and the pipe 27, and enters the flow path _10b2 of the air cooler 10b in the air cooling period. The low-pressure raw material air flowing in the counterflow is cooled, and the air itself is heated and then led out, enters the first refrigerant pump 15 through the valve 46, is discharged under pressure, and enters the warmer 3. The first circulating refrigerant heated in the warmer 3 is passed through the valve 47 and the pipe 4.
8. The air cooler 1 in the regeneration phase via the valve 49
0a, the waste nitrogen in the flow path _{10a 1 flowing} countercurrently is heated, and then the waste nitrogen itself is cooled and led out, and is again introduced into the first LNG heat exchanger 14 through the valves 51 and 29, and the same process continues. circulate. The other flow path 10a ₁ of the air cooler 10a in the regeneration period includes the nitrogen heat exchanger 2.
1 is introduced through the pipe 34, the pipe 52, and the valve 53, and as the temperature rises, the moisture deposited on the pipe wall of the flow path _10a1 evaporates and is led out.
5 and then released out of the system. The temperature conditions of each flow path of each heat exchanger and cooler in this cycle correspond to the previous cycle. Also like this air cooler 10
When a is in the regeneration period and the air cooler 10b is in the air cooling period, valves 41, 43 (low pressure raw material air system path), valve 4
4, 46, 47, 49, 51, 29 (first circulating refrigerant system) and valves 53, 54 (waste nitrogen system) are open, and valves 37, 35, 12 (low pressure raw air system) are open. , valves 28, 26, 50, and 31 (first circulating refrigerant line), and valve 9 (waste nitrogen line) are closed.
Conversely, as mentioned above, the air cooler 10a is in the air cooling period,
When 10b is in the regeneration period, valves 9, 12 (low pressure raw material air system path), valves 31, 49, 50, 26, 28, 2
9 (first circulation refrigerant system line), valves 35 and 37 (waste nitrogen system line) are open, and valves 54, 53, and 43 are open.
(Low pressure raw material air system line), valves 44, 46, 47, 51
(first circulating refrigerant line) and valve 41 (waste nitrogen line) are closed. These valves are all automatic switching valves, and are configured to open and close automatically when switching between the air cooling period and the regeneration period. FIGS. 2 and 3 show the valve opening/closing states and the direction of fluid flowing through each channel in the above two periods. The switching interval for both periods is 10 to 15 minutes.

Next, the reason why it is necessary to perform cooling and moisture removal using the air coolers that are used in pairs as described above will be explained below. The reversing heat exchanger and regenerator normally installed in air liquefaction separation equipment have a raw air pressure of about 5 kg/cm ² , and the water and waste nitrogen for purging carbon dioxide gas have atmospheric pressure. Therefore, precipitated water,
Due to this pressure difference, carbon dioxide gas can be sufficiently purged even if the temperature of the purging waste nitrogen is lower than the raw air temperature. However, when both the feed air and the waste nitrogen for purging are close to atmospheric pressure, moisture cannot be completely purged with the waste nitrogen because the outlet temperature of the waste nitrogen is lower than the inlet temperature of the feed air in a normal heat exchange method. Figure 4 shows the relationship between moisture content and pressure. Pressure 1 atm, temperature 0℃,
The respective water saturation contents at 2℃ and 15℃ are X ₁ ,
Assuming X ₂ and X ₃ , there is a relationship of X ₁ < X ₂ < X ₃ , so
When the outlet temperature of the waste nitrogen for purging is 0° C. and the raw air inlet temperature is 2° C. (Δt=2° C.), the moisture content is X ₁ <X ₂ , and this moisture cannot be completely purged. However, if the outlet temperature of the waste nitrogen for purging is 2° C. or higher, purging can be easily performed. Generally, when purging moisture and carbon dioxide gas, it is necessary to consider purge efficiency, but in the present invention, regeneration (moisture purge) is carried out so that the moisture precipitated by the waste nitrogen for purging can be completely removed. At the same time, while flowing the refrigerant heated to about 20°C by the heater 3 into the flow path 10a ₂ or 10b ₂ of the air cooler, waste nitrogen for purging is flowed into the other flow path 10a ₁ or 10b _1. While exchanging and heating, the moisture that was precipitated by the flow of raw material air in the previous cycle is purged. When the amount of waste nitrogen is 60% of the amount of air, the inlet temperature of air cooler 10a or 10b is approximately -120°C,
The outlet temperature is 15℃. This outlet temperature of 15°C is a temperature that has a sufficient margin to purge the moisture content of the raw air when the inlet temperature is 2°C.

In addition to the raw material air, other waste heat sources in the factory, such as compression heat for pressurizing product gas from an air separation device, can also be used as a heating source for moisture purging in the case of regeneration.

Energy savings that can be achieved by compressing air at low temperatures using the method described above are as follows. In the case of an air liquefaction separation device that produces 12,000 m ³ /h of oxygen gas, air at a temperature of 30°C and humidity of 80% is
The power unit to compress up to Kg/cm ² is approximately 0.09KWH/m ³
Alr. The power consumption rate decreases in proportion to the compressor inlet temperature, so by performing low-temperature compression at -140℃, it becomes 0.09×273−140/273+30=0.0395KWH/m ³ Air, which is approximately 44% (1 /2.3). In other words, the electricity consumption rate can be reduced by 56%. Therefore, the oxygen gas is 12,000 m ³ /h, and the amount of raw air is 65,000
In the case of large equipment such as m ³ /h, this energy saving value is enormous, with annual operating hours of 8000
This effect is approximately 2.6×10 ⁷ KWH in terms of time, which is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the method of the present invention;
FIGS. 2 and 3 are system diagrams showing details of the low-temperature dehumidification process of the present invention, and FIG. 4 is a diagram showing the relationship between moisture content and pressure. 2 is an air blower, 3 is a warmer, 5 is an air precooler, 6 is a water separator, 10a, 10b are air coolers, 14 is the first LNG heat exchanger, 15 is the first refrigerant circulation pump, 16 is the air 17 is a compressed air cooler, 18 is a second LNG heat exchanger, 19 is a second refrigerant circulation pump, 21 is a nitrogen heat exchanger, and 22 is an air liquefaction separation device.

Claims (1)

[Claims] 1. Introducing raw air into a warmer using a raw air blower, exchanging heat with a circulating refrigerant, and then cooling it with low-temperature compressed air in an air precooler to lower the temperature;
The raw air is introduced into one of a pair of air coolers that are used selectively and cooled by the circulating refrigerant, and moisture is solidified and precipitated in the flow path to be removed, resulting in low-temperature dry air, which is then sent to an air compressor. The low-temperature compressed feed air is introduced into a nitrogen heat exchanger to exchange heat with nitrogen from the air liquefaction separation device to raise the temperature, and then to the air precooler. A step of introducing the refrigerant and raising the temperature to almost room temperature and then introducing it into the air separation device, and introducing the refrigerant cooled by the liquefied natural gas heat exchanger to the warmer through the air cooler and raising the temperature, forming a circulating refrigerant which is introduced into the other air cooler to raise the temperature of the nitrogen from the nitrogen heat exchanger and is then returned to the liquefied natural gas heat exchanger; A low-temperature compression method for raw air for an air liquefaction separation device, comprising a step of melting and evaporating moisture that has precipitated and solidified in the previous cycle to remove it along with it.