JP3220755B2 - Air liquefaction separation method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air liquefaction separation method and apparatus, and more particularly, to air for rectifying and separating raw material air in response to fluctuations in demand for product gas or product liquefied gas and differences in power rates between day and night. The present invention relates to an air liquefaction separation method and apparatus capable of efficiently operating a rectification column in a rectification separation section while maintaining operating conditions in an optimum state.

[0002]

2. Description of the Related Art Conventionally, oxygen, nitrogen,
Production of various gases such as argon and liquefied gases has been performed. In such an air liquefaction / separation device, various devices configured to cope with fluctuations in demand for product oxygen gas and product nitrogen gas have been developed.

For example, in the apparatuses described in Japanese Patent Publication No. 61-51233 and Japanese Patent Laid-Open Publication No. Hei 3-63490, a liquefied oxygen storage tank, a liquefied nitrogen storage tank, and a liquefied air storage tank are used to cope with fluctuations in demand for product oxygen gas. Equipment such as liquefied oxygen, liquefied nitrogen, and liquefied air are introduced and led out as needed.

However, in the above-described apparatus, when the demand for oxygen gas fluctuates, the flow direction of the liquefied gas is reversed, the flow rate of the expansion turbine is changed in order to adjust the amount of cooling, or the supply of raw air is performed. It is necessary to change the amount.

[0005] As a result, the flow rate of each part changes and the operating conditions in the rectification column change, so that not only the rectification efficiency may decrease, but also each part operates stably in response to fluctuations in oxygen gas demand. There was a problem that it took time until it came to be.

Therefore, an air liquefaction / separation apparatus that collects a large amount of liquefied gas requires a large amount of refrigeration to operate the apparatus. It is known that a liquefaction cycle section is provided, and the liquefied gas produced in the gas liquefaction cycle section is supplied into a rectification column as a cold source of an air rectification separation section.

FIG. 4 shows a general system of an air liquefaction / separation apparatus having the above-mentioned gas liquefaction cycle section. The compressed and purified raw air is supplied from the pipe 1 to the air rectification separation section A.
After being cooled by exchanging heat with the return gas, it is introduced into the lower tower 3 of the rectification tower, where the nitrogen gas at the top of the lower tower and the oxygen at the bottom of the lower tower are rectified by the rectification. Separate with enriched liquefied air.

[0008] The oxygen-enriched liquefied air at the bottom of the lower tower is withdrawn through a pipe 4 and introduced into a middle stage of an upper tower 7 via a subcooler 5 and a pressure reducing valve 6. The nitrogen gas in the upper part of the lower tower 3 is liquefied in the main condensing evaporator 8 to become liquefied nitrogen, which becomes a reflux liquid of the lower tower 3 and a part thereof is connected to the supercooler 5, the pressure reducing valve 10 through the pipe 9.
The liquid is introduced into the top of the upper tower 7 via the pipe 11, and a part of the liquid is further stored as liquefied nitrogen in the liquefied nitrogen storage tank 13 through the pipe 11 and the valve 12.

The oxygen-enriched liquefied air and liquefied nitrogen introduced into the upper tower 7 are separated into high-purity nitrogen gas at the top of the upper tower and liquefied oxygen at the bottom of the upper tower by rectification in the upper tower 7. The high-purity nitrogen gas at the top of the upper tower is extracted into a pipe 14, passes through the subcooler 5 and the main heat exchanger 2, and is collected as a product nitrogen gas via a valve 15 and a pipe 16. The product liquefied oxygen is extracted from the bottom of the upper tower 7 by a pipe 17, and the oxygen gas evaporated by the main condensing evaporator 8 is extracted from the pipe 18, and the product is passed through the main heat exchanger 2 and the pipe 19. Collected as Furthermore, from the middle stage of the upper tower 7,
Exhaust gas is extracted by the pipe 20 and discharged through the subcooler 5, the main heat exchanger 2, and the pipe 21.

On the other hand, part of the nitrogen gas extracted from the top of the upper tower 7 to the pipe 14 and collected from the pipe 16 is:
Before the valve 15, it branches into a pipe 22, and is introduced into the gas liquefaction cycle section B through a valve 23. This nitrogen gas is first compressed to a high pressure by the compressors 24 and 25, and the first circulation heat exchanger 2
6. After being cooled by exchanging heat with the return gas in the second circulation heat exchanger 27, the gas is introduced from the expansion valve 28 into the gas-liquid separator 29.

The nitrogen gas branched to the pipe 30 at the outlet of the first circulating heat exchanger 26 is expanded by the expansion turbine 31 to generate cold, and then extracted from the gas-liquid separator 29 to the pipe 32. After being returned to room temperature by the second circulation heat exchanger 27 and the first circulation heat exchanger 26 from the pipe 33 after being merged with the nitrogen gas, it is returned to the middle stage of the compressors 24 and 25.

The liquefied nitrogen in the gas-liquid separator 29 is supplied to the pipe 34 and the valve 35 as a cold source of the air rectifying / separating section A.
, A predetermined amount is constantly supplied to the middle stage of the lower tower 3.

In the air liquefaction / separation apparatus configured as described above, 60 to 70% of the total power consumption of the equipment is consumed in the gas liquefaction cycle section B, which occupies most of the operation cost.

On the other hand, electric power for driving a compressor or the like is as follows:
The night time is cheaper than the day time. Therefore, it is desirable to operate the compressor as much as possible during the daytime and to increase the amount of operation at nighttime. Therefore, also in the above-described air liquefaction / separation apparatus, if the gas liquefaction cycle section B is operated only during the time period when the nighttime electricity rate is low, the power consumption of the entire facility can be significantly reduced.

However, in the above-described apparatus configuration, the liquefied nitrogen liquefied in the gas liquefaction cycle section B is directly supplied to the lower tower 3. Therefore, when the gas liquefaction cycle section B is stopped in the daytime, the air rectification separation section A The cold source is lost, and the operation of the device cannot be continued.

The above-described gas liquefaction cycle unit can be incorporated in the above-mentioned demand fluctuation type apparatus. In this case, too, the operation state of the gas liquefaction cycle unit is changed in response to fluctuations in product demand. It is necessary to change the flow rate of each part, or change the flow rate of each part. Therefore, similarly to the above, the state of the air rectification separation part changes, the separation efficiency decreases, and it takes a long time until the operation state is stabilized. There is.

Therefore, the present invention provides a gas liquefaction cycle which does not change the state of the air rectification and separation section even when the output of the product is changed due to fluctuations in demand for the product (various gas and liquefied gas). An air liquefaction separation method and apparatus that can operate the air rectification separation section in a stable state even when stopped during a time period when daytime power rates are high, and can efficiently use power to reduce operation costs. It is intended to provide.

Further, the present invention provides an air liquefaction / separation apparatus having the above-mentioned liquefaction cycle section, which simplifies the operation of starting and stopping the liquefaction cycle section, shortens the required time, and reduces the time required in the rectification column. It is another object of the present invention to provide an air liquefaction / separation method and apparatus capable of preventing state fluctuations and efficiently producing air.

[0019]

In order to achieve the above-mentioned object, the air liquefaction separation method of the present invention comprises the steps of:
In an air liquefaction separation method for purifying, cooling and rectifying to separate oxygen, nitrogen and the like, a nitrogen gas after heat exchange with the raw material air in an air rectifying / separating section having no cold generation means.
The liquefied gas is introduced into the gas liquefaction cycle unit, liquefied, and the obtained liquefied gas is stored in a storage tank, and a predetermined amount of the liquefied gas in the storage tank is separated by the air rectification separation unit. Characterized in that the gas liquefaction cycle section is supplied at all times as a cold source for operation to the section.
Only the liquefied gas in the storage tank is supplied to the air rectification and separation section by one of the two main and sub liquefied gas pumps, and during the operation switching time of the main and sub liquefied gas pumps. The liquefied gas required by the air rectification and separation unit is stored in advance on the downstream side of the liquefied gas pump.

The air liquefaction / separation apparatus of the present invention comprises an air rectification / separation unit having no cold generating means for compressing, purifying, cooling and rectifying raw air to separate oxygen, nitrogen and the like; Nitrogen gas after heat exchange with the raw material air in the rectification separation section
A branch pipe that leads a part of the air from the air rectification separation section,
A gas liquefaction cycle unit for liquefying the nitrogen gas derived from the manifold, a storage tank for storing the liquefied gas liquefied in the gas liquefaction cycle unit, and a predetermined amount of the liquefied gas in the storage tank operated by the air rectification separation unit And a liquefied gas supply system that constantly supplies a liquefied gas supply system as a cold source for use. Further, the liquefied gas supply system is provided with two main and sub liquefied gas pumps, one of which is operated. Downstream of the secondary liquefied gas pump, a storage tank for storing the liquefied gas required by the air rectifying and separating unit during the operation switching time of the liquefied gas pump is provided, and a perforated plate is provided in the storage tank. And

[0021]

[Operation] According to the above configuration, even if the operation of the gas liquefaction cycle section is changed or temporarily stopped, the rectified gas stored in the storage tank is always kept at a predetermined amount in the air rectification separation section. Since the air is supplied, the operation of the air rectification and separation section can be continued under stable conditions without change. For example, when the demand for oxygen gas or nitrogen gas decreases, the gas liquefaction cycle unit is operated, an operation is performed such that excess gas is liquefied and stored in a storage tank as a liquefied gas, and when the demand for gas increases. In such a case, it is possible to perform an operation in which the gas liquefaction cycle unit is stopped and the gas derived from the air rectification separation unit is sent out as a total product gas. In this case, since a predetermined amount of cold required by the air rectification and separation unit is constantly supplied from the storage tank, the state of the air rectification and separation unit does not change. That is, it is possible to simplify the operation at the time of these switchings, to shorten the time, and to prevent a change in the state of the rectification column.

Further, the gas liquefaction cycle section is operated during a time period when the nighttime electricity rate is low, and the obtained liquefied gas is stored in a storage tank while being supplied to the air rectification separation section, so that the daytime electricity rate is high. By stopping the gas liquefaction cycle section and using the liquefied gas in the storage tank during the time period, the air liquefaction / separation apparatus can be efficiently operated using inexpensive power.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the embodiments shown in the drawings. In the following description,
The same components as those of the conventional device shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

First, in FIG. 1, the air rectification separation section A and the gas liquefaction cycle section B are configured substantially in the same manner as the apparatus shown in FIG. From the pipe 1 through the main heat exchanger 2 to the rectification tower consisting of the lower tower 3 and the upper tower 7, where it is rectified and separated from the pipe 14.
, A product liquefied oxygen from the pipe 17, a product oxygen gas from the pipe 18, and an exhaust gas from the pipe 20. The high-purity nitrogen gas derived from the pipe 14 is
After heat exchange with the raw material gas in the main heat exchanger 2,
It is collected as product nitrogen gas.
Part of the gas is led to a pipe 22 that branches off from the pipe 16 to liquefy gas.
Introduced to cycle section B.

The gas liquefaction cycle section B includes a branch pipe 2
2 through the compressors 24, 25,
Circulating heat exchangers 26 and 27, expansion valve 28, gas-liquid separator 29
And liquefied by the expansion turbine 31 and extracted from the valve 35.

In the apparatus of this embodiment, a storage tank 51 for storing the liquefied nitrogen derived from the valve 35 is provided.
A liquefied gas supply system having a liquefied gas pump 52 for sending out the liquefied nitrogen in 1 and a pressure reducing valve 53 is provided. That is, while liquefied nitrogen derived from the valve 35 is stored in the storage tank 51, the air rectification separation section A is stored in the storage tank 51.
Liquefied nitrogen corresponding to the required amount of refrigeration is sent out by a liquefied gas pump 52, and the pressure is reduced by a pressure reducing valve 53 to a pressure corresponding to the pressure of the upper tower 7 in FIG. I have. When the pressure in the storage tank 51 is sufficiently high, the liquefied gas pump 52 may be omitted.

The gas liquefaction cycle section B constructed as described above
By appropriately setting the liquefaction capacity and the capacity of the storage tank 51, it is possible to always supply a constant amount of liquefied nitrogen to the air rectification and separation section A regardless of the operation state of the gas liquefaction cycle section B. For example, the gas liquefaction cycle section B is operated during the night when the power rate is low to store liquefied nitrogen in the storage tank 51, and the gas liquefaction cycle section B is stopped during the day when the power rate is high and the liquefied nitrogen in the storage tank 51 is converted to air. It can be supplied to the rectification separation section A.

In the case where the demand for the product nitrogen gas fluctuates, when the demand amount of the product nitrogen gas sent out from the pipe 16 decreases, excess high-purity nitrogen gas is supplied from the pipe 22 to the gas liquefaction cycle section. By introducing it into B and liquefying it, it is possible to supply a required amount of product nitrogen gas to a demand destination without wastefully discharging high-purity nitrogen gas or changing the operation state of the rectification column. . on the other hand,
When the demand amount of the product nitrogen gas is the maximum, the gas liquefaction cycle section B can be stopped and the entire amount of the high-purity nitrogen gas derived from the pipe 14 can be sent out as a product.

Further, since the demand for the product nitrogen gas is usually large in the daytime and small in the nighttime, even in the above-mentioned case, the inexpensive power at night can be effectively used.

The liquefied nitrogen in the storage tank 51 can be taken out as a product as required, or can be sent by vaporization as a backup when demand increases. Further, in order to cope with fluctuations in the demand for oxygen, oxygen gas is introduced into the gas liquefaction cycle section B for liquefaction, or oxygen gas is liquefied using the liquefied nitrogen obtained in the gas liquefaction cycle section B as a cold source. As described above, the heat exchanger, the liquefied oxygen storage tank, and the piping may be appropriately provided.

Next, in the embodiment shown in FIG. 2, a sub-pump 52a is provided in consideration of a failure of the liquefied gas pump 52, and a buffer storage tank 54 is provided downstream of the liquefied gas pumps 52, 52a.

As shown in detail in FIG. 3, the buffer storage tank 54 is provided with a separating plate 60 made of a perforated plate or the like at an intermediate position in the storing tank 54, and the upper and lower parts of the separating plate 60 are provided by the separating plate 60. Liquids with temperature differences are prevented from mixing.
That is, the liquefied nitrogen supplied into the storage tank 54 has a pressure in the liquefied nitrogen storage tank 51 of about 0.3 kg / cm ² G and the saturated liquid is pressurized by the liquefied gas pump 52, so It is liquid. Therefore, the supply liquid is supplied to the separator 60.
And the gas is not supplied to the gas layer above the storage tank 54, and the pipe 56 is only connected to the lower tower 3.

Further, by providing the sub-pump 52a as described above, when the main liquefied gas pump 52 is stopped due to a failure or the like and the supply of liquefied nitrogen is switched to the sub-pump 52a, until the sub-pump 52a operates stably, that is, The liquefied nitrogen required by the air rectification and separation unit A during the operation switching time of the liquefied gas pump can be covered by the liquefied nitrogen in the buffer storage tank 54.

Therefore, even if the liquefied gas pump 52 breaks down, a constant amount of liquefied gas can be continuously supplied to the air rectifying and separating section A, and a stable state can be obtained without changing the operating conditions of the rectifying tower. The operation can be continued.

Next, an example of an operation state of the embodiment apparatus shown in FIG. 2 will be described. 5.5kg / cm ² by raw material air compressor
The raw material air 10000 Nm ³ / h, which has been compressed to G and from which water and carbon dioxide have been removed by the pretreatment equipment, is introduced into the main heat exchanger 2 of the air rectification and separation section A by the pipe 1 and exchanges heat with the return gas. Thereby, it is cooled to -170 ° C and introduced into the lower tower 3 of the rectification column.

The raw air introduced into the lower tower 3 is separated by rectification, and liquefied nitrogen 3800 Nm ³ /
h, 6200 Nm ³ / h of oxygen-enriched liquefied air is withdrawn from the pipe 4. The liquefied nitrogen extracted from the pipe 9 is supercooled to −188 ° C. by exchanging heat with the return gas in the supercooler 5, and then from the storage tank 51 via the liquefied gas pump 52, the buffer storage tank 54, and the pressure reducing valve 53. And liquefied nitrogen 1300 Nm ³ / h supplied from the pipe 55 and introduced into the upper part of the upper tower 7. The oxygen-enriched liquefied air extracted from the pipe 4 is also supercooled to -178 ° C. by the supercooler 5 and then introduced into the upper tower 7.

The liquefied nitrogen and oxygen-enriched liquefied air are separated by the rectification of the upper tower 7, and the product liquefied oxygen 900 Nm ³ / h from the pipe 17 and the product oxygen gas 110
0 Nm ³ / h, high-purity nitrogen gas 8200 Nm from pipe 14
³ / h, and 1100 Nm ³ / h of exhaust gas are withdrawn from the pipe 20. The high-purity nitrogen gas and the exhaust gas extracted from the pipes 14 and 20 are subjected to heat exchange in the
In the main heat exchanger 2, heat exchange with the raw material air is carried out together with the oxygen gas from the furnace, the temperature of the raw material air becomes room temperature, and the product air and the exhaust gas are sent out.

The high-purity nitrogen gas sent out from the pipe 14 is sent as a product at 200 Nm ³ / h through the pipe 16, and 8000 Nm ³ / h is branched to the pipe 22 and supplied to the gas liquefaction cycle part B for liquefaction nitrogen. Introduced as gas. This nitrogen gas is first compressed by the compressor 24, and then joins with the circulating return nitrogen gas 72,000Nm ³ / h from the pipe 33,
Further, it is compressed to 50 kg / cm ² G by the compressor 25. The high-pressure nitrogen gas of 80,000 Nm ³ / h is subjected to heat exchange with the return gas in the first circulating heat exchanger 26 to −100 ° C.
9500 Nm ³ / h was further cooled to −162 ° C. by exchanging heat with the return gas in the second circulation heat exchanger 27, and then 8.5 kg / h at the expansion valve 28.
It is expanded under reduced pressure to cm ² G and introduced into the gas-liquid separator 29 where it is separated into nitrogen gas and liquefied nitrogen.

The nitrogen gas 70500 Nm ³ / h branched to the pipe 30 at the outlet of the first circulating heat exchanger 26 is entropy-expanded to 8.5 kg / cm ² G by the expansion turbine 31 to generate cold. The nitrogen gas 1500 Nm ³ / h extracted from the gas-liquid separator 29 to the pipe 32 is
From 3, heat is exchanged with nitrogen gas for liquefaction in the second circulating heat exchanger 27 and the first circulating heat exchanger 26, and after returning to room temperature, it is returned to the middle stage of the compressors 24 and 25.

On the other hand, 8000 Nm ³ / h of liquefied nitrogen separated by the gas-liquid separator 29 is sent to the storage tank 51 and stored as liquefied nitrogen for cold source and product liquefied nitrogen in the air rectification separation section A.

The liquefied nitrogen in the storage tank 51 is 1300 Nm ³
/ H is pressurized to 7 kg / cm ² G by the liquefied gas pump 52 and sent out. The gas is constantly supplied to the upper tower 7 from the pipe 55 through the buffer storage tank 54 having a capacity of 0.5 m ³ and the pressure reducing valve 53. Note that, in this example, the gas phase is connected to the lower tower 3 by a pipe 56 in order to maintain the pressure in the buffer storage tank 54.

When the demand for the product nitrogen gas increases, the operation of the gas liquefaction cycle section B is stopped, and all the nitrogen gas branched to the pipe 22 is sent out from the pipe 16 so that 8200 Nm ³ / h of high-purity nitrogen gas. At this time, since the liquefied nitrogen in the storage tank 51 is supplied to the rectification tower as a cold source in the same manner as described above, the operation state of the rectification tower is constant, and the operation is continued in an optimal state. be able to.

When the power rate is taken into consideration, the above-mentioned operation is performed during a time period when the power rate is low, that is, at night or on holidays, and during the time when the power rate is high in the daytime, the gas liquefaction cycle section B is stopped. In addition, it is possible to perform an operation using electric power effectively, and it is possible to greatly reduce the power source unit of the product.

Further, even when the gas liquefaction cycle section B is operated and stopped, a constant amount of liquefied nitrogen, which is a cold source, is always supplied to the rectification column, so that there is no change in the state when the operation is switched. .

Therefore, when the operation mode is switched, the operation can be completed within a short period of time without complicating the operation. In addition, when the mode is switched, the state of the rectification / separation section A is changed to the liquefaction cycle section. Stable operation can be continued without being affected by the state change of B at all.

The configurations of the air rectification section A and the gas liquefaction cycle section B can be appropriately optimized according to the type of the product to be collected. That is, in this embodiment, the case where the nitrogen gas is liquefied has been described.
The present invention can also be applied to the case where oxygen is liquefied and stored and introduced into a rectification tower, or the storage and introduction of liquefied air. The effect is great when the air liquefaction / separation section A does not have the cold generating means, but the same can be applied to the case where the cold liquefying means is provided. In particular, since the present invention can always keep the operation state of the rectification column constant, it is possible to collect argon with high efficiency by applying it to an air liquefaction / separation apparatus equipped with an argon collection system.

[0047]

As described above, according to the present invention,
It is possible to change the amount of product delivered without changing the operation state of the air rectification and separation unit including the rectification tower at all, and to operate according to the difference in electricity rates between day and night. The required amount of product can be always manufactured in a stable state at low cost without the influence of the above.

[Brief description of the drawings]

FIG. 1 is a system diagram of an air liquefaction / separation apparatus showing one embodiment of the present invention.

FIG. 2 is a system diagram of an air liquefaction / separation apparatus showing another embodiment of the present invention.

FIG. 3 is an enlarged view of a buffer storage portion.

FIG. 4 is a system diagram showing an example of a conventional air liquefaction / separation apparatus.

[Explanation of symbols]

2 heat exchanger 3 lower tower 7 upper tower 24
25 Compressor 26 First circulation heat exchanger 27 Second circulation heat exchanger
29 gas-liquid separator 31 expansion turbine 51 storage tank 52 liquefied gas pump 53 pressure reducing valve 54 buffer storage tank A air rectification separation section B gas liquefaction cycle section

Claims (6)

(57) [Claims] 1. A compressed feed air, purified, cooled and fractionated, oxygen in cryogenic air separation method for separating nitrogen or the like, wherein the cold generating means at no air rectifying separation unit Hara
Fractionation of nitrogen gas after heat exchange with feed air by air rectification
From the gas liquefaction cycle section to liquefy,
An air liquefaction separation method comprising storing the obtained liquefied gas in a storage tank and constantly supplying a predetermined amount of the liquefied gas in the storage tank to the air rectification and separation unit as a cold source for operation. 2. The air liquefaction separation method according to claim 1, wherein the gas liquefaction cycle section is operated only during a specific time zone. 3. The liquefied gas in the storage tank is supplied to the air rectification / separation unit by one of the main and sub liquefied gas pumps, and the air rectification / separation unit is operated during the operation switching time of the main and sub liquefied gas pumps. 2. The air liquefaction separation method according to claim 1, wherein the liquefied gas required by the method is stored in advance on the downstream side of the liquefied gas pump. 4. An air rectification and separation unit which does not have a cold generating means for compressing, purifying, cooling and rectifying the raw air to separate oxygen, nitrogen and the like, and the air rectification and separation unit And the raw material air
Part of the nitrogen gas after heat exchange is introduced from the air rectification separation section.
A branch pipe for discharging, a gas liquefaction cycle unit for liquefying the nitrogen gas derived from the branch pipe, a storage tank for storing the liquefied gas liquefied in the gas liquefaction cycle unit, and a predetermined amount of the liquefied gas in the storage tank. A liquefied gas supply system which constantly supplies a liquefied gas as an operation cold source to the air rectification and separation unit. 5. The liquefied gas supply system is provided with two main and sub liquefied gas pumps, one of which is operated, and the other is provided downstream of the main and sub liquefied gas pumps during the operation switching time of the liquefied gas pump. 5. A storage tank for storing a liquefied gas required by the rectifying / separating section is provided.
An air liquefaction separation device as described. 6. The air liquefaction / separation apparatus according to claim 5, wherein the liquefied gas storage tank provided on the downstream side of the liquefied gas pump has a perforated plate provided in the stored liquid.