JPH0476380A - Method and device for air separation suitable for fluctuation of demand - Google Patents

Abstract

PURPOSE:To keep the condition of a fractionating tower best at all times, obtain respective product gas with a high obtaining rate and cope with the fluctuation of demand with simple device and structure by a method wherein a liquefied oxygen producing means and an amount of nitrogen gas control means are operated to regulate so that the evaporating amount of the liquefied oxygen becomes an amount corresponding to the producing amount of nitrogen gas produced by the liquefying of the nitrogen gas while the amount of nitrogen gas, produced from a sub fractionating tower, is controlled so as to be kept in constant. CONSTITUTION:When the demand of product oxygen gas is reduced, a pressure in a product oxygen supplying conduit 11 is increased in accordance with the reduction of said demand whereby the pressure regulator 36a of a liquefied oxygen producing means is operated to choke a control valve 36b in accordance with the increasing amount of the pressure. Accordingly, the amount of introduction of the liquefied oxygen from a liquefied oxygen storage tank 13 is reduced and the evaporating amount of a sub heat exchanger 14 is reduced whereby the amount of product oxygen gas, supplied to the demanding source, can be reduced. In this case, a nitrogen gas amount control means is operated to increase the introducing amount of nitrogen gas into a nitrogen gas indroducing tube 19 and maintain the condition of an auxiliary fractionating tower 6 in constant.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air separation method and device suitable for demand fluctuations, and more specifically, the present invention relates to an air separation method and device suitable for demand fluctuations. This invention relates to a separation method and apparatus.

[Conventional technology]

Various methods and devices have been proposed in the past as means for increasing or decreasing the amount of oxygen or nitrogen obtained from an air separation device in response to fluctuations in demand.

For example, in the air separation device described in Japanese Patent Publication No. 49-45998, when the demand for product oxygen gas decreases, the amount of oxygen gas drawn out from the upper column of the rectification column is reduced, and , the amount of liquefied oxygen led out from the upper tower is increased and stored in the liquefied oxygen storage tank, and conversely, when the demand for product oxygen gas increases, the amount of oxygen gas led out from the upper tower is increased, and the amount of oxygen gas led out from the upper tower is increased and stored in the liquefied oxygen storage tank. The liquefied oxygen in the distillation column is vaporized with nitrogen gas derived from the lower column of the rectification column to produce oxygen gas, which is then combined with the oxygen gas obtained from the upper column of the rectification column. Furthermore, the liquefied nitrogen that is liquefied when the liquefied oxygen in the liquefied oxygen storage tank is vaporized is first stored in the liquefied nitrogen storage tank and then introduced into the upper tower as a reflux liquid from the upper tower.

[Problem to be solved by the invention]

However, in the above method, the ratio of oxygen gas and liquefied oxygen derived from the upper column changes due to fluctuations in the demand for product oxygen gas, and the amount of nitrogen gas derived from the lower column and the amount of reflux liquid in both the upper and lower columns changes. As a result, the pressure inside the rectification column and the rectification balance became unstable, resulting in a decrease in efficiency.

In particular, in air separation equipment in which a crude argon column is attached to the upper column in order to extract argon, disturbances in the rectification balance in the upper column have a large effect on the argon extraction efficiency, so the argon yield can be significantly reduced. Sometimes it made things worse.

In addition to the above publications, several methods and devices have been proposed, but all of them change the state of the rectification column, so
The reality is that demand fluctuations are responded to by sacrificing the yield of each product gas to some extent.

Therefore, the present invention has developed an air separation system that can keep the rectification column in the best condition, obtain each product gas, especially argon gas, at a high yield, and can respond to demand fluctuations with a simple equipment configuration. The present invention aims to provide methods and apparatus.

[Means to solve the problem]

In order to achieve the above object, the present invention introduces a certain amount of oxygen gas derived from the upper column of the rectification column into the main heat exchanger to exchange heat with the raw material air, and recovers the temperature to around room temperature. At the same time, a certain amount of liquefied oxygen is derived from the upper column and introduced into a liquefied oxygen storage tank, and the liquefied oxygen in the liquefied oxygen storage tank is derived in response to fluctuations in demand for the product oxygen gas. , introduced into the auxiliary heat exchanger and vaporized by exchanging heat with nitrogen gas, which will be described later. The vaporized oxygen gas is combined with the product oxygen gas, and a certain amount of nitrogen gas is drawn out from the rectification column and branched. and introducing nitrogen gas in an amount corresponding to the vaporized amount of the liquefied oxygen into the auxiliary heat exchanger to liquefy it, or introducing the branched nitrogen gas into the auxiliary heat exchanger to reduce the vaporized amount of the liquefied oxygen. In addition to providing an air separation method suitable for demand fluctuations, which is characterized by liquefying an amount of nitrogen gas according to the amount of nitrogen gas, introducing the liquefied liquefied nitrogen into a liquefied nitrogen storage tank, and leading the remaining nitrogen gas out of the system. In order to maintain a constant state of the rectification column, there is a feed air amount control means that controls the feed air amount to a constant level during steady operation, and a feed air amount control means that controls the liquid level of the liquefied air at the bottom of the lower column of the double rectification column to a constant level. Alternatively, a liquefied air amount control means for controlling the flow rate of the liquefied air to the upper column at a constant level, and a liquefied air amount control means for controlling the liquid level of the liquefied oxygen in the main condenser at a constant level, or leading the liquefied oxygen to a liquefied oxygen storage tank. liquefied nitrogen amount control means for controlling the amount of liquefied oxygen at a constant level; liquefied nitrogen amount control means for controlling the amount of liquefied nitrogen introduced from the liquefied nitrogen storage tank to the top of the upper column at a constant level; and a nitrogen gas amount control means that controls the pressure or flow rate of the nitrogen gas derived from the lower column and/or the upper column to be constant, and also according to fluctuations in the demand for product oxygen gas. The present invention provides an air separation device suitable for demand fluctuations, characterized in that it is provided with liquefied oxygen deriving means for deriving and vaporizing liquefied oxygen from the liquefied oxygen storage tank.

[For production]

Therefore, even if the product gas is increased or decreased according to demand fluctuations, a constant amount of gas and liquid is always drawn out from the rectification column, and a corresponding amount of raw material air, reflux liquid, etc. is introduced. The rectification condition in the rectification column can always be maintained in the best condition.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on the flow of each gas and liquid, with reference to an embodiment of the air separation device shown in the drawings.

First, in FIG. 1, raw air is compressed by a compressor 1, introduced into an adsorber 3 via a cooling device 2, and after removing impurities such as moisture and carbon dioxide contained therein, it is introduced into a cold box 4. be done. The raw air introduced into the cold box 4 is cooled by exchanging heat with various return gases in the main heat exchanger 5, and then introduced into the lower part of the lower column 7 of the double rectification column 6. By the rectification operation in the lower column 7, the feed air is separated into nitrogen gas at the top of the lower column and oxygen-enriched liquefied air (hereinafter referred to as liquefied air) at the bottom of the lower column. 7 and introduced into the middle stage of the upper column 9 via the expansion valve 31b, and is separated into nitrogen gas at the top of the upper column and liquefied oxygen and oxygen gas at the bottom of the upper column by rectification in the upper column 9.

In addition, a part of the nitrogen gas is liquefied in the main condenser 28,
It is led out from the lower column 7 and introduced into the top of the upper column 9 via the valve 8, and becomes the reflux liquid of the upper column 9.

From this double rectification column 6, separated oxygen gas, liquefied oxygen, and nitrogen gas are each led out in fixed amounts. That is, the oxygen gas at the bottom of the upper tower is led out through the conduit 10 and introduced into the main heat exchanger 5, and after exchanging heat with the raw air and recovering the temperature to around normal temperature, it is supplied to the demand from the product oxygen supply conduit 11. be done.

The amount of oxygen gas extracted from this product shall be set according to the standard usage amount. If there is a time period when the amount of oxygen gas used is zero when demand decreases, the entire amount will be extracted with liquefied oxygen, and the amount of oxygen gas extracted will be constant. The operating conditions are set using the case where the amount is zero as the standard.

The liquefied oxygen at the bottom of the upper column is led out through a conduit 12 and introduced into a liquefied oxygen storage tank 13, and is led out from the liquefied oxygen storage tank 13 in response to fluctuations in demand for product oxygen gas.
In step 4, heat exchange is performed with nitrogen gas, which will be described later, and after vaporization, the product oxygen gas is merged with the product oxygen gas in the product oxygen supply conduit 11.

On the other hand, the high-purity product nitrogen gas led out from the top of the upper column 9 is introduced into the conduit 15, and is led out of the system through the main heat exchanger 5 at room temperature, like the oxygen gas mentioned above. Also,
The low-purity nitrogen gas led out from the upper part of the upper column 9 to the conduit 15a is led out of the system through the main heat exchanger 5 in the same manner as described above. A portion of this low-purity nitrogen gas may be used as a product gas, and a portion may be released as waste gas after being used for regeneration of the adsorber 3 or the like.

A part of the high-purity nitrogen gas led out from the upper part of the lower column 7 to the conduit 16 is branched to the conduit 17, and further part of it is used as a heat source for vaporizing liquefied oxygen in the auxiliary heat exchanger 14, After being liquefied, it is introduced into the liquefied nitrogen storage tank 18. The amount of nitrogen gas used as a heat source is determined by introducing the amount required for vaporizing the liquefied oxygen into the auxiliary heat exchanger 14, or by supplying an amount in excess of the amount equivalent to the vaporization, and uncomposed components are recycled from the liquefied nitrogen storage tank. It may also be discharged through the secondary heat exchanger 14 and into the conduit 19.

The liquefied nitrogen in the liquefied nitrogen storage tank 18 is constantly drawn out in fixed amounts from the bottom and introduced into the top of the upper column 6 as a reflux liquid. This fixed amount of liquefied nitrogen may be introduced into the lower column 7 and merged into a line leading from the top of the lower column 7 to the top of the upper column 9 via the valve 8. Further, high-purity nitrogen gas other than that introduced into the auxiliary heat exchanger 14 is led out of the system from a high-purity nitrogen gas outlet pipe 19.

Further, the remaining constant amount of the high-purity nitrogen gas led out from the lower column 7 is temporarily recovered to near normal temperature in the main heat exchanger 5, or after the temperature is recovered, a constant amount is branched and sent to the expansion turbine 20. After being introduced into the brake blower 21 and pressurized, it is introduced into the main heat exchanger 5 from the hot end, cooled to an intermediate temperature, led out from the middle part of the main heat exchanger 5, and introduced into the expansion turbine 20. . The high-purity nitrogen gas expanded and cooled by the expansion turbine 20 joins the high-purity product nitrogen gas led out from the top of the upper column 9 and is again introduced into the main heat exchanger 5, where it is cooled and recovered before being discharged from the system. is derived. By doing so, the amount of nitrogen extracted from the lower column 7 can be reduced and the yield of argon, which will be described later, can be increased. Note that the nitrogen gas introduced into the expansion turbine 20 is
Not only the high-purity nitrogen gas at the top of the lower column 7, but also a certain amount of low-purity nitrogen gas from an arbitrary number of stages below the top may be led out and supplied to the expansion turbine 20 through the same route as above.

Further, a crude argon column 22 is attached to this double rectification column 6. A fixed amount of argon raw material gas from the middle and lower part of the upper column is introduced into the crude argon column 22 through a conduit 23, and after being rectified, a fixed amount of crude argon is led out from a conduit 24 at the top of the column. The liquefied oxygen whose argon content has been reduced by the rectification in the crude argon column 22 is passed from the bottom of the column to the conduit 25.
After that, it is returned to the upper tower. Further, a part of the liquefied air drawn out from the bottom of the lower column 7 is branched and introduced into the condenser 26 provided at the top of the crude argon column 22 via an expansion valve 27. The liquefied air is introduced into the upper column 9 after being partially vaporized.

This air separation apparatus is provided with various automatic control means in order to maintain a constant operating state of the double rectification column 6 and to respond to fluctuations in the demand for product oxygen gas. first,
The raw material air supply system includes a flow rate regulator 30 as a raw material air amount control means for controlling the raw material air amount to a constant level during steady operation.
a and a compressor air volume regulator 30b or suction guide vane. The liquefied air system includes a liquid level as a liquefied air amount control means that controls the liquid level of the liquefied air at the bottom of the lower column 7 to be constant, or controls the flow rate of the liquefied air to the upper column 9 to be constant. A total of 31a and a control valve 31b are provided. The liquefied oxygen lead-out system at the bottom of the upper column 9 includes a liquefied oxygen system that controls the level of liquefied oxygen in the main condenser 28 to a constant level, or controls the amount of liquefied oxygen led out to the liquefied oxygen storage tank 13 to a constant level. Liquid level gauge 3 as a quantity control means
28 and a control valve 32b are provided. A system for introducing liquefied nitrogen from the liquefied nitrogen storage tank 18 to the top of the upper column 9 is provided with a flow regulator 33a and a control valve 33b as liquefied nitrogen amount control means for controlling the amount of liquefied nitrogen at a constant level. A system for introducing oxygen gas from the lower part of the upper column is provided with a flow rate regulator 34a and a control valve 34b as oxygen gas amount control means for controlling the flow rate of the oxygen gas at a constant level. The system for deriving nitrogen gas from the lower column 7 includes a pressure regulator 35a and a control valve 35b as nitrogen gas amount control means for controlling the pressure or flow rate of the nitrogen gas at a constant level, and a control valve 35b for controlling the flow rate of the expansion turbine. A flow rate regulator 35C and a control valve 35d are provided.

A system for deriving and vaporizing liquefied oxygen from the liquefied oxygen storage tank 13 in response to fluctuations in demand for product oxygen gas includes a liquefied oxygen deriving means that operates in response to pressure changes within the product oxygen supply conduit 11. Pressure regulator 36a and control valve 36
b is provided.

Next, a description will be given of how the air separation apparatus configured as described above responds to fluctuations in the demand for the product oxygen gas.

First, when the demand for product oxygen gas increases, the pressure inside the product oxygen supply conduit 11 decreases with the increase in demand, so the pressure regulator 36a of the liquefied oxygen deriving means is activated to reduce the pressure. The control valve 36b is opened depending on the amount of decrease. As a result, the inside of the product oxygen supply conduit 11 and the liquefied oxygen storage tank 13
The liquefied oxygen is led out to the conduit 29 and introduced into the secondary heat exchanger 14 due to the pressure difference between the inside and outside, where it exchanges heat with the nitrogen gas introduced into the secondary heat exchanger 14, vaporizes and becomes oxygen gas, and produces the product. It joins the product oxygen gas in the oxygen supply conduit 11 and is supplied to the demand destination. When liquefied oxygen is introduced into the secondary heat exchanger 14,
The amount of liquefied nitrogen gas introduced into the auxiliary heat exchanger] 4 as a heat source for vaporizing liquefied oxygen increases, and the pressure inside the nitrogen gas outlet pipe 19 decreases, so that the pressure regulator 35a of the nitrogen gas amount control means is actuated to throttle the control valve 35b so that the amount of nitrogen gas introduced into the auxiliary heat exchanger 14 corresponds to the amount of vaporized liquefied oxygen, and the pressure inside the outlet pipe 19 is kept constant. On the other hand, the amount of nitrogen gas supplied to the expansion turbine 20 is always kept constant by the flow rate regulator 35C3 control valve 35d. Therefore, the amount of branched nitrogen derived from the lower column 7 is kept constant, and even if a part of the nitrogen gas derived from the lower column 7 is liquefied, the pressure and flow rate of the nitrogen gas derivation system 16 will not change. The amount of nitrogen gas discharged from the upper part of the lower column is kept constant.

On the other hand, when the demand for product oxygen gas decreases, the pressure within the product oxygen supply conduit 11 increases due to the decrease in demand, so the pressure regulator 36a of the liquefied oxygen deriving means operates to increase the pressure. The control valve 36b is throttled according to the amount. As a result, the amount of liquefied oxygen drawn out from the liquefied oxygen storage tank 13 is reduced, and the amount of vaporized in the auxiliary heat exchanger 14 is reduced, so that the amount of product oxygen gas to be supplied to customers can be reduced.

At this time as well, the nitrogen gas amount control means operates to increase the amount of nitrogen gas delivered to the nitrogen gas delivery pipe 19 and to maintain the state of the double rectification column 6 constant.

During the above fluctuation period, both the high-purity product nitrogen gas led out from the top of the upper column 9 through the conduit 15 and the low-purity nitrogen gas led out from the top of the upper column 9 through the conduit 15a are maintained at a constant flow rate. A control means may be provided to maintain a constant flow rate of these gases, but manual operation may also be used.

Therefore, in response to fluctuations in the demand for product oxygen gas, the liquefied oxygen deriving means and the nitrogen gas amount control means operate, and both control the vaporized amount of liquefied oxygen and the amount of nitrogen gas derived by liquefying nitrogen gas. At the same time, the amount of nitrogen gas led out from the double rectifier 6 is controlled to be constant, so the amount of product oxygen gas supplied can be adjusted while keeping the condition of the double rectifier 6 constant. can be adjusted. At the same time, since each of the control means is always in operation, the operating conditions of each part are always kept in the best condition, making it possible to operate with the highest yield. In particular, since the condition inside the upper column 9 can be kept constant, the composition of the argon-enriched gas introduced into the crude argon column 22 can be kept constant, and impurity components such as nitrogen and oxygen contained in the obtained crude argon. can be reduced and the yield of crude argon can be improved.

Furthermore, as shown in this embodiment, it is possible to respond to demand fluctuations without installing ancillary equipment including rotating equipment such as compressors and refrigerators, so there is no need to start or stop these equipment. In addition to reducing the construction cost of the device, it is also possible to reduce the operating cost. In addition, since the condition of the rectification column is always kept constant, the rotating equipment installed in the air separation equipment can always be operated at a constant rotation and load, making it easy to control and reducing fluctuations in throughput. Since there is no need for equipment, it is possible to install equipment of the minimum necessary size, which also reduces costs.

In the above embodiment, an example was explained in which the demand for oxygen gas fluctuates. However, as is clear from the above description, as the product oxygen gas increases or decreases, the amount of nitrogen gas discharged from the nitrogen gas discharge pipe also changes. Therefore, in response to changes caused by fluctuations in the amount of nitrogen gas demanded, such as changes in the pressure of the nitrogen gas outlet pipe,
By linking the liquefied oxygen deriving means and the nitrogen gas amount control means, it is possible to easily respond to fluctuations in the demand for nitrogen gas.

Here, in the air separation apparatus having the above configuration, the average demand amount of the product oxygen gas is about 20,000 Nrrr/h.

The results of calculating the operating conditions for a facility in which the demand fluctuation range is 24,000 to 9,000 NrrIl/h and the demand increase time is about 6 hours and the demand decrease time is about 2 hours out of 8 hours will be explained.

First, the amount of raw air is approximately 100,000 Nrr? /h
The amount of oxygen is approximately 9000 as oxygen gas.
N/h, approximately 1100ONr//h as liquefied oxygen,
The oxygen gas is constantly led out from each rectification column, and the entire amount of oxygen gas is always supplied as product oxygen gas to the demand end from the product oxygen supply conduit.

When the demand decreases, all of the liquefied oxygen is stored in the liquefied oxygen storage tank, so the supply amount of product oxygen gas is 900%.
ONrrl'/h. At this time, a part of the nitrogen gas led out from the rectification column, 1700O
Nitrogen gas of Nrrr/h is led out.

When demand increases, the amount of liquefied oxygen in the liquefied oxygen storage tank increases to 1,500 ml.
ONrrl'/h vaporizes and merges with the product, increasing the supply amount of product oxygen gas to 24,000 Nrr? /h. At this time, a total amount of 17,000 Nrd/h of nitrogen gas, which corresponds to 1,500 ONr/h of liquefied oxygen, is introduced into the auxiliary heat exchanger to become liquefied nitrogen and introduced into the liquefied nitrogen storage tank.

In addition, the liquefied nitrogen in the liquefied nitrogen storage tank is always 1300 ON.
rrl'/h is introduced into the upper column as reflux liquid.

Figure 2 shows the flow rate changes in the main parts at this time.

As mentioned above, the demand for product oxygen gas can be easily met by simply opening and closing the valves according to pressure changes in the product oxygen supply pipe and nitrogen gas outlet pipe while keeping the gas-liquid balance constant in the rectification column. It can respond to fluctuations and has a wide range of responses.

FIG. 3 shows another embodiment of the present invention, in which the present invention is applied to an apparatus that boosts the pressure of product nitrogen gas using a booster 40 and sends it out. That is, from the top of the upper column 9 to the conduit 1
The product nitrogen gas led out to step 5 is pressurized by a pressure booster 40 and sent to a product nitrogen conduit 41, and a part of the product nitrogen gas after pressure increase is branched and introduced into the auxiliary heat exchanger 14 to convert the liquefied oxygen into Use as a heating source. Further, the conduit 15 is provided with a flow rate regulator 35e, a regulating valve 35f, or a pressure regulator to keep the amount of product nitrogen gas led out from the top of the upper column 9 constant and to keep the condition inside the upper column 9 constant. I try to keep it that way. As a result, the amount of nitrogen extracted from the lower column 7 can be reduced and the yield of argon can be increased.
Power consumption can be minimized.

Further, FIGS. 4 and 5 show still another embodiment of the present invention. That is, the temperature at which the liquefied oxygen is vaporized in the secondary heat exchanger 14 is set to the temperature on the cold end side of the main heat exchanger 5, and the secondary heat exchanger 14 only exchanges latent heat. Therefore, the nitrogen gas is introduced into the auxiliary heat exchanger 14 without being introduced into the main heat exchanger 5, and the oxygen gas vaporized in the auxiliary heat exchanger 14 is sent to the consumer after its temperature is recovered in the main heat exchanger 5. Sent. The only difference between FIG. 4 and FIG. 5 is that the secondary heat exchanger 14 in FIG. 5 is of a condenser type.

In addition, in FIGS. 3, 4, and 5 above, only the main parts of the air separation device are shown, and the same components as those in the embodiment shown in FIG. Further explanations will be omitted.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to respond to demand fluctuations while keeping the condition of the rectification column constant, so it is possible to optimize rectification efficiency and product yield, and reduce product cost and power source. units can be reduced. In addition, since there is no need to install equipment such as compressors and refrigerators in areas that respond to demand fluctuations, equipment costs can be reduced, as well as power and maintenance costs, and equipment reliability and operability can be improved. It is also excellent.

Furthermore, it has excellent adaptability to fluctuation amounts and fluctuation patterns.

In particular, in air separation equipment equipped with a crude argon column, maintaining the condition of the upper column constant is a major factor in increasing the yield of crude argon. In addition to efficiently responding to demand fluctuations, argon can also be efficiently extracted at the same time, making it possible to obtain various product gases at lower locations.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of the air separation device of the present invention, FIG. 2 is a diagram showing flow rate changes when demand fluctuates, and FIG. 3 is a system diagram showing another embodiment of the present invention. 4 and 5 are system diagrams showing still other embodiments of the present invention.

Claims (1)

[Claims] 1. Air separation in which raw air is compressed, carbon dioxide gas and moisture are removed, the air is cooled by heat exchange with return gas, and the air is introduced into a rectification column to collect oxygen, nitrogen, etc. as products. In the method, a certain amount of oxygen gas derived from the upper column of the rectification column is introduced into the main heat exchanger to exchange heat with the raw material air, and the temperature is recovered to around room temperature, and at the same time, it is taken out as product oxygen gas. ,
Deriving a certain amount of liquefied oxygen from the upper column and introducing it into a liquefied oxygen storage tank, and leading out the liquefied oxygen in the liquefied oxygen storage tank according to demand fluctuations of the product oxygen gas and introducing it into a secondary heat exchanger,
It is vaporized by heat exchange with nitrogen gas, which will be described later, and the vaporized oxygen gas is combined with the product oxygen gas, and a certain amount of nitrogen gas is derived from the rectification column and branched, depending on the amount of vaporized liquefied oxygen. Introducing an amount of nitrogen gas into the secondary heat exchanger to liquefy it, or introducing the branched nitrogen gas into the secondary heat exchanger to liquefy an amount of nitrogen gas corresponding to the amount of vaporization of the liquefied oxygen. , an air separation method suitable for demand fluctuations, characterized by introducing liquefied nitrogen into a liquefied nitrogen storage tank and leading the remaining nitrogen gas out of the system. 2. The air separation method suitable for demand fluctuations according to claim 1, wherein the nitrogen gas derived from the rectification column is nitrogen gas derived from the lower column. 3. After the nitrogen gas led out from the lower column is heated in the main heat exchanger, at least a certain amount of it is branched, or after branched, the nitrogen gas is heated in the main heat exchanger and then heated in the brake blower of the expansion turbine. It is characterized by introducing it into the main heat exchanger to increase the pressure, cooling it to an intermediate temperature in a main heat exchanger, leading it out, introducing it into an expansion turbine to expand and lower the temperature, and then introducing it into the main heat exchanger again to perform cold recovery. An air separation method suitable for demand fluctuations according to claim 2. 4.Equipped with a raw air compressor, an adsorber for removing impurities, a main heat exchanger, a double rectification tower, a liquefied oxygen storage tank, a liquefied nitrogen storage tank, etc., and collects oxygen, nitrogen, etc. by liquefying and rectifying the raw air. In the separation equipment, in order to maintain the condition of the rectification column constant,
Feed air amount control means for controlling the feed air amount to a constant level during steady operation, and controlling the liquid level of the liquefied air at the bottom of the lower column of the double rectification column to be constant, or the flow rate of the liquefied air to the upper column to be constant. liquefied oxygen amount control means for controlling the liquefied air amount to a constant level in the main condenser or for controlling the amount of liquefied oxygen delivered to the liquefied oxygen storage tank; liquefied nitrogen amount control means for controlling the amount of liquefied nitrogen introduced from the nitrogen storage tank to the top of the upper column at a constant level; Alternatively, a nitrogen gas amount control means is provided to control the pressure or flow rate of the nitrogen gas derived from the upper tower to a constant level, and liquefied oxygen is derived from the liquefied oxygen storage tank and vaporized according to fluctuations in demand for product oxygen gas. An air separation device suitable for demand fluctuations, characterized by being equipped with an oxygen deriving means. 5. The air separation device suitable for demand fluctuations according to claim 4, further comprising: an auxiliary heat exchanger for exchanging heat between liquefied oxygen and nitrogen gas derived from the liquefied oxygen storage tank to vaporize the liquefied oxygen; An air separation device suitable for demand fluctuations, characterized by being provided with a regulating means for adjusting the amount of oxygen and the amount of nitrogen gas to corresponding amounts. 6. The air separation apparatus suitable for demand fluctuations according to claim 4, characterized in that the nitrogen gas derived from the upper column is high purity nitrogen gas and/or low purity nitrogen gas. Air separation equipment.