JP2024063690A - Operation method of nitrogen production device - Google Patents

Abstract

To provide an operation method that can further reduce the power consumption of a nitrogen production device which industrially produces nitrogen by using cryogenic liquefaction/separation and also can further reduce power source unit.SOLUTION: A operation method of a so-called double-tower nitrogen production device having a first rectification tower 8 and a second rectification tower 51 for collecting product nitrogen by cryogenically liquefying and separating compressed, rectified, and cooled material air, repeats a liquid collecting operation which extracts at least a part of first liquefied nitrogen obtained in the first rectification tower 8 and introduces it into a liquefied nitrogen storage tank 80, and a liquid injection operation which injects the liquefied nitrogen into the second rectification tower 51 from the liquefied nitrogen tank 80 via a liquefied nitrogen injection path 72 and stops operation of an expansion turbine 24.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for operating a nitrogen production apparatus, and more specifically, to a method for operating a nitrogen production apparatus that separates and refines raw air using a cryogenic liquefaction separation method to extract product nitrogen (nitrogen gas, liquid nitrogen).

In the industrial production of nitrogen, a method of air liquefaction separation using cryogenic liquefaction separation is often used. As a method of industrially producing nitrogen using cryogenic liquefaction separation, a nitrogen production method employing a two-tower nitrogen production apparatus process has been disclosed (see, for example, Patent Documents 1 and 2).

The nitrogen production methods disclosed in Patent Documents 1 and 2 use a twin-column nitrogen production system equipped with two rectification towers, and introduce waste gas from one of the rectification towers, which is discarded in a single-column nitrogen production system process using a single-column nitrogen production system equipped with only one rectification tower, as raw material for the other rectification tower, making it possible to significantly improve product yield and power consumption.

Figure 1 is a system diagram showing an example of the equipment configuration of a so-called two-tower nitrogen production equipment equipped with two rectification towers, which is also used in Patent Document 1. Using this diagram, the basic conventional operating method will be explained.

First, this nitrogen production apparatus comprises a first fractionator 8 that performs low-temperature distillation of the raw air that has been pressurized to a predetermined pressure by a raw air compressor 3, purified by a pretreatment adsorption unit 4, and then cooled by a main heat exchanger 6 in a cold-storage outer tank 5, to separate the raw air into a first nitrogen gas at the top of the tower and a first oxygen-enriched liquefied fluid at the bottom of the tower; a first condenser 13 that performs indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid reduced in pressure by a pressure reducing valve 16 to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen, and at the same time, evaporates and gasifies the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid; a second fractionator 51 that performs low-temperature distillation of a portion of the first oxygen-enriched gas fluid, to rectify and separate the second nitrogen gas at the top of the tower and the second oxygen-enriched liquefied fluid at the bottom of the tower; The second condenser 58 indirectly exchanges heat with the second oxygen-enriched liquefied fluid depressurized by the pressure valve 63 to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and at the same time evaporates and gasifies the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid; a first product recovery path 11 that discharges a portion of the first nitrogen gas as a first product nitrogen gas after heat recovery; a second product recovery path 56 that discharges a portion of the second nitrogen gas as a second product nitrogen gas after heat recovery; a first oxygen-enriched liquefied fluid merging path 61 that connects the lower part of the first fractionator 8 and the lower part of the second fractionator 51 via a valve 62; an expansion turbine 24 that adiabatically expands a portion of the first oxygen-enriched gas fluid; and a nitrogen compressor 54 that compresses the second product nitrogen gas.

This nitrogen production device also includes liquefied nitrogen injection paths 71, 72 that introduce liquefied nitrogen stored in a liquefied nitrogen storage tank 80 into the first fractionator 8 and the second fractionator 51.

Next, we will explain the basic operation of this equipment. First, the raw air taken in through path 1 and filter 2 is compressed to a specified pressure by raw air compressor 3, and purified by pretreatment adsorber 4 to remove impurities such as moisture and carbon dioxide. After that, the air is cooled to a specified temperature by exchanging heat with product nitrogen gas and waste gas in main heat exchanger 6 in outer refrigerated tank 5.

The compressed, purified, and cooled feed air is introduced from the main heat exchanger 6 through the feed air inlet path 7 into the bottom of the first fractionator 8, where it is separated into a first nitrogen gas at the top of the tower and a first oxygen-enriched liquefied fluid at the bottom of the tower by low-temperature distillation using a cryogenic liquefaction separation method in the first fractionator 8.

In the first fractionator 8, the compressed, purified, and cooled feed air is introduced into the bottom of the tower through the feed air inlet path 7, and is separated into a first nitrogen gas at the top of the tower and a first oxygen-enriched liquefied fluid at the bottom of the tower by low-temperature distillation using a cryogenic liquefaction separation method in this first fractionator 8.

A portion of the first nitrogen gas extracted from the top of the tower to path 9 branches off to path 10 and exchanges heat with the feed air in main heat exchanger 6, and after heat recovery, is discharged as first product nitrogen gas from first product recovery path 11. The remaining first nitrogen gas is introduced into first condenser 13 through path 12.

The first oxygen-enriched liquefied fluid, which has been extracted from the bottom of the first fractionator 8 and reduced to a predetermined pressure by the pressure reducing valve 16, is introduced into the first condenser 13 through a path 17, and the first oxygen-enriched liquefied fluid and the first nitrogen gas exchange heat indirectly with each other, so that the first nitrogen gas condenses and liquefies to become the first liquefied nitrogen, and at the same time, the first oxygen-enriched liquefied fluid evaporates and gasifies to become the first oxygen-enriched gas fluid. The first liquefied nitrogen is introduced into the top of the first fractionator 8 through a path 14 and becomes the reflux liquid.

On the other hand, the first oxygen-enriched gas fluid discharged from the first condenser 13 to the path 18 is partially branched off to the path 50 toward the second fractionator 51, and a very small portion of the remaining part is depressurized by the valve 19 and branched off to the path 20, where it exchanges heat with the feed air in the main heat exchanger 6 to recover heat, and is discharged as waste gas from the waste gas discharge path 21.

The first oxygen-enriched gas fluid that is not branched into path 50 and path 20 is introduced into the main heat exchanger 6 through path 22, heated to an intermediate temperature, and extracted into path 23. It flows into the expansion turbine 24 and undergoes adiabatic expansion to generate the cold necessary to operate the device, and then merges with the first oxygen-enriched gas fluid in path 20. After heat recovery in the main heat exchanger 6, it is discharged as waste gas from the waste gas discharge path 21.

The first oxygen-enriched gas fluid introduced from line 50 into the bottom of the second fractionator 51 is separated into a second nitrogen gas at the top of the tower and a second oxygen-enriched liquefied fluid at the bottom of the tower by low-temperature distillation in the second fractionator 51. A portion of the second nitrogen gas extracted from the top of the tower into line 52 branches off into line 53 and exchanges heat with the feed air in the main heat exchanger 6. After heat recovery, the second nitrogen gas is compressed to a predetermined pressure by the nitrogen compressor 54 and discharged as a second product nitrogen gas from the second product recovery line 56. The remaining second nitrogen gas is introduced into the second condenser 58 through line 57.

In this second condenser 58, the second oxygen-enriched liquefied fluid extracted from the bottom of the second fractionator 51 and the first oxygen-enriched liquefied fluid extracted from the bottom of the first fractionator 8 and branched off into the first oxygen-enriched liquefied fluid merging path 61 are merged, and then the pressure is reduced by the pressure reducing valve 63 and introduced from the path 64 at a predetermined temperature. The second oxygen-enriched liquefied fluid and the second nitrogen gas after merging perform indirect heat exchange, and the second nitrogen gas condenses and liquefies to become the second liquefied nitrogen, and at the same time, the second oxygen-enriched liquefied fluid evaporates and gasifies to become the second oxygen-enriched gas fluid. The second liquefied nitrogen is introduced into the top of the second fractionator 51 through the path 59 and becomes the reflux liquid.

Meanwhile, the second oxygen-enriched gas fluid discharged from the second condenser 58 to the path 65 is depressurized by the valve 66 and then merges with the path 20, where it exchanges heat with the raw air in the main heat exchanger 6 to recover heat, and is then discharged as waste gas from the waste gas discharge path 21.

The first product recovery path 11 and the second product recovery path 56 merge downstream to form a single path 70, from which the first product nitrogen gas and the second product nitrogen gas are discharged.

The above is the configuration of a two-tower nitrogen production system and its basic operating method. In the operating method of FIG. 1 (Patent Document 1), the liquefied nitrogen stored in the liquefied nitrogen storage tank 80 can be introduced into the first fractionator 8 or the second fractionator 51 depending on the operating state of the system and the amount of refrigeration required, thereby providing the refrigeration source required for the operation of each fractionator.

Patent No. 3738213 Patent No. 4451438

However, nitrogen production equipment that uses cryogenic liquefaction separation to produce nitrogen industrially consumes a large amount of power, so there is a demand for further reduction in the unit size.

In response to such demands, the present invention aims to provide an operating method for a nitrogen production system that can further reduce power consumption and power unit consumption.

In order to achieve the above object, the method of operating the nitrogen production apparatus of the present invention includes a first fractionation column that performs low-temperature distillation of compressed, purified, and cooled feed air to separate it into a first nitrogen gas in the upper part of the column and a first oxygen-enriched liquefied fluid in the bottom part of the column; a first condenser that performs indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen and at the same time evaporate and gasify the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid; a second fractionation column that performs low-temperature distillation of at least a portion of the first oxygen-enriched gas fluid to separate it into a second nitrogen gas in the upper part of the column and a second oxygen-enriched liquefied fluid in the bottom part of the column; and a second condenser that performs indirect heat exchange between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen and at the same time evaporate and gasify the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid. A method for operating a nitrogen production apparatus including a nitrogen extractor, an expansion turbine into which a portion of the first oxygen-enriched gas fluid is introduced, a first product recovery path for extracting a portion of the first nitrogen gas as a first product nitrogen gas after heat recovery, a second product recovery path for extracting a portion of the second nitrogen gas as a second product nitrogen gas after heat recovery, a first liquefied nitrogen discharge path for extracting at least a portion of the first liquefied nitrogen and introducing it into a liquefied nitrogen storage tank, and a liquefied nitrogen injection path for introducing liquefied nitrogen from the liquefied nitrogen storage tank into the second rectification tower, the method being characterized by alternately repeating a liquid collection operation in which at least a portion of the first liquefied nitrogen is extracted from the first liquefied nitrogen discharge path, and a liquid injection operation in which liquefied nitrogen is introduced from the liquefied nitrogen storage tank into the second rectification tower and the operation of the expansion turbine is stopped.

In addition, in the method of operating the nitrogen production apparatus of the present invention, it is preferable that the amount of feed air introduced into the first fractionator during the liquid injection operation is less than the amount of feed air introduced into the first fractionator during the liquid collection operation.

Furthermore, in the method of operating the nitrogen production apparatus of the present invention, it is preferable that the amount of the second product nitrogen gas in the liquid injection operation is greater than the amount of the second product nitrogen gas in the liquid collection operation.

According to the present invention, the average power consumption of the nitrogen production equipment can be reduced by alternately repeating a conventional basic operation, a liquid extraction operation that can extract liquid nitrogen with approximately the same amount of power as the basic operation, and a liquid injection operation that can reduce power with approximately the same amount of air and product as the conventional basic operation. By switching between the liquid extraction operation and the liquid injection operation according to the power demand, it is possible to reduce power or store the difference in power consumption as liquefied nitrogen.

FIG. 1 is a system diagram showing an example of a nitrogen production apparatus implementing a conventional basic operation method. FIG. 2 is a system diagram showing a liquid collection operation of the nitrogen production apparatus used in the embodiment, to which the method of operating the apparatus according to the present invention is applied. FIG. 2 is a system diagram showing a liquid injection operation to which the method of operating the apparatus according to the present invention of the nitrogen production apparatus used in the embodiment is applied.

Below, a two-tower nitrogen production apparatus according to one embodiment of the present invention and an operating method of the nitrogen production apparatus will be described with reference to Figures 2 and 3. In the following description, components that are the same as those of the nitrogen production apparatus shown in Figure 1 and have the same functions are given the same reference numerals, and detailed descriptions, including the operating method, will be omitted.

The nitrogen production apparatus shown in Figures 2 and 3 is a nitrogen production apparatus that extracts product nitrogen by cryogenic liquefaction separation of feed air, just like that shown in Figure 1, and is a so-called two-tower nitrogen production apparatus equipped with two rectification towers. Note that the nitrogen production apparatus shown in Figure 1 differs from that shown in Figure 1 in that the apparatus in Figure 1 is equipped with a liquefied nitrogen injection path 71 for introducing liquefied nitrogen from the liquefied nitrogen storage tank 80 to the first rectification tower 8, whereas the nitrogen production apparatus shown in this embodiment is equipped with a first liquefied nitrogen discharge path 15 that branches off from path 14 and introduces a portion of the first liquefied nitrogen into the liquefied nitrogen storage tank 80.

The so-called two-column nitrogen production system is composed of distillation columns with different operating pressures. That is, the first oxygen-enriched liquefied fluid collected from the bottom of the first distillation column 8 is depressurized and vaporized to become a first oxygen-enriched gas fluid, which is introduced into the second distillation column 51, so the operating pressure of the second distillation column 51 is lower than that of the first distillation column 8.

The operating method of the nitrogen production device in this embodiment is not the basic operation described above, but rather controls each part to alternate between liquid collection operation and liquid injection operation as described below. The liquid collection operation and liquid injection operation are switched between alternately as appropriate to reduce the average power consumption.

(Liquid collection operation)
First, the liquid collection operation of the present invention will be described with reference to Fig. 2. In the liquid collection operation, unlike the basic operation described above, the first liquefied nitrogen liquefied in the first condenser 13 is introduced into the upper part of the first rectification column 8 through the line 14 to become a reflux liquid, but a part of it is extracted from the first liquefied nitrogen discharge line 15 and sent to the liquefied nitrogen storage tank 80. In the liquid collection operation, the first liquefied nitrogen is collected in addition to the first product nitrogen gas, so when the same first product nitrogen gas as in the basic operation is to be collected, the amount of feed air needs to be increased compared to the basic operation.

(Liquid injection operation)
Next, the liquid injection operation of the present invention will be described with reference to FIG. 3. In the liquid injection operation, unlike the basic operation described above, the operation of the expansion turbine 24 is stopped, and liquefied nitrogen is used instead as a cold source. In this case, liquefied nitrogen is sent from the liquefied nitrogen storage tank 80 to the upper part of the second fractionator 51 through the liquefied nitrogen injection path 72. As described above, the first oxygen-enriched liquefied fluid collected from the lower part of the first fractionator 8 is depressurized and vaporized to become the first oxygen-enriched gas fluid, which is introduced into the second fractionator 51, so that the operating pressure of the second fractionator 51 is lower than that of the first fractionator 8. Therefore, the liquefied nitrogen sent from the first fractionator 8 to the liquefied nitrogen storage tank 80 through the first liquefied nitrogen discharge path 15 can be introduced into the second fractionator 51 through the liquefied nitrogen injection path 72 without using a liquid pump.

In addition, since the expansion turbine 24 is stopped during liquid injection operation, the entire amount of the first oxygen-enriched gas fluid is introduced into the second fractionator 51 via path 50.

The amount of feed air introduced into the first fractionator 8 during liquid injection operation is less than the amount of feed air introduced into the first fractionator 8 during liquid collection operation. Also, the amount of second product nitrogen gas during liquid injection operation is greater than the amount of second product nitrogen gas during liquid collection operation.

In the operating method of the nitrogen production apparatus in this embodiment, a liquid collection operation in which at least a portion of the first liquefied nitrogen is extracted from the first liquefied nitrogen discharge path and a liquid injection operation in which at least a portion of the first liquefied nitrogen extracted in the liquid collection operation is injected into the second fractionator 51 from the liquefied nitrogen injection path 72 and the operation of the expansion turbine 24 is stopped are switched between and alternately repeated as appropriate.

(When used primarily for liquid collection)
Table 1 shows a comparison between a case where basic operation was performed for 24 hours and a case where liquid collection operation was the main operation, in which liquid collection operation was performed for 15 hours a day and liquid injection operation was performed for 9 hours a day.

When this liquid extraction operation is the main operation, the power is 655 kW, which is almost the same as in basic operation, but 888 ^Nm3 of liquefied nitrogen can be extracted. When liquid extraction operation is the main operation, 0.4% of the air volume of liquid nitrogen can be extracted with almost the same power as in basic operation.

(When liquid injection is the main operation)
Table 2 shows a comparison between a case where basic operation was performed for 24 hours and a case where liquid sampling operation was performed for 10 hours and liquid injection operation was performed for 14 hours each day as the main operation.

When liquid injection operation is the main operation, ⁹⁵² Nm3 will be injected for the ¹⁰⁰⁰ Nm3 of liquefied nitrogen extracted in liquid extraction operation, but the total power required is 635 kW, which is a 3% reduction in power compared to basic operation's 654 kW. When liquid injection operation is the main operation, the produced liquid is almost entirely used for injection, making it possible to reduce power by 3% compared to basic operation.

In liquid injection operation, it is possible to reduce power consumption with roughly the same amount of air and product as in basic operation, and in liquid collection operation, liquid nitrogen can be collected with roughly the same amount of power as in basic operation. Therefore, if the device is operated by appropriately switching between liquid collection operation and liquid injection operation as in the embodiment, it is possible to further reduce the power consumption of the device used when industrially producing nitrogen using the cryogenic liquefaction separation method, and further reduce the power unit.

In this embodiment, the liquefied nitrogen sent from the first rectification column 8 to the liquefied nitrogen storage tank 80 through the first liquefied nitrogen discharge path 15 can be introduced into the second rectification column 51 through the liquefied nitrogen injection path 72 without using a liquid pump, so the power required for liquid injection can be reduced. In addition, in a conventional single rectification column, when liquefied nitrogen is extracted from the rectification column, the pressure of the liquefied nitrogen storage tank is lower than the operating pressure of the rectification column, so a liquid pump is required to inject the liquefied nitrogen.

In addition, in liquid injection operation, the expansion turbine 24 is stopped, so that the first oxygen-enriched gas fluid can be introduced into the second fractionator 51. Since the second fractionator 51 has a high relative volatility and a high product yield due to its low operating pressure, the increased amount of oxygen-enriched gas fluid introduced allows a larger amount of second product nitrogen gas to be collected. In liquid injection operation, the amount of feed air can be reduced compared to when the same amount of product nitrogen gas is collected in basic operation, and the feed air compressor 3 can be operated at a reduced volume compared to basic operation. On the other hand, the power of the nitrogen compressor 54 increases due to the increase in the second product nitrogen gas. However, since the impact of the reduction in the power of the feed air compressor 3, which accounts for the majority of the power of the device, is large, the average power can be reduced when viewed from the perspective of the entire device.

In addition, since liquid collection operation collects liquefied nitrogen in addition to the product nitrogen gas, if the same product nitrogen gas as in basic operation is to be collected, the amount of raw air must be increased compared to basic operation. This increases the power of the raw air compressor 3, and the power required for liquid collection operation becomes greater, but by combining it with liquid injection operation, the effect of the increased power can be offset. Therefore, by appropriately switching between liquid injection operation and liquid collection operation, it is possible to collect more liquefied nitrogen with roughly the same power and the same amount of product nitrogen gas as in basic operation.

In addition, by performing this type of liquid collection operation, it becomes possible to store surplus electricity in the form of liquid nitrogen. In other words, liquid collection operation is basically performed at night when electricity demand is low and electricity rates are low, and liquid nitrogen is stored, and liquid injection operation is performed during the day to consume the collected liquid nitrogen, thereby reducing electricity costs.

The revised Energy Conservation Act, which came into force in April 2021, adds the concept of "leveling electricity demand," and stipulates that measures that contribute to leveling electricity demand, such as saving electricity and shifting the time of electricity use, will be taken nationwide between 8:00 and 22:00 from July to September (summer) and December to March (winter). In response to this, demand response (a mechanism in which end consumers themselves change their electricity usage from their normal electricity consumption patterns in response to time-varying electricity prices, or rewards designed to reduce electricity usage when wholesale electricity prices rise or supply and demand are tight) is expected to be utilized, and by performing liquid extraction/liquid injection operations as in this embodiment, it is possible to further reduce electricity charges by introducing demand response, which can also contribute to stabilizing the power grid.

The nitrogen production device shown in this embodiment is only one example, and the drawings do not necessarily reflect all the configurations of the nitrogen production device. Furthermore, the operation method can be not only repeated liquid sampling operation and liquid injection operation, but also appropriately combined with basic operation, etc.

Reference Signs List 1: Path, 2: Filter, 3: Feed air compressor, 4: Pretreatment adsorber, 6: Main heat exchanger, 8: First fractionator, 11: First product recovery path, 13: First condenser, 15: First product liquefied nitrogen discharge path, 16: Pressure reducing valve, 21: Waste gas discharge path, 24: Expansion turbine, 51: Second fractionator, 54: Nitrogen compressor, 56: Second product recovery path, 58: Second condenser, 61: First oxygen-enriched liquefied fluid joining path, 63: Pressure reducing valve, 72: Liquefied nitrogen injection path, 80: Liquefied nitrogen storage tank

Claims (3)

a first fractionator for cryogenically distilling the compressed, purified and cooled feed air into a first nitrogen gas in an upper portion of the first fractionator and a first oxygen-enriched liquefied fluid in a bottom portion of the first fractionator;
a first condenser that performs indirect heat exchange between the first nitrogen gas and the first oxygen-enriched liquefied fluid to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen and simultaneously evaporates and gasifies the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid;
a second fractionator for cryogenically distilling at least a portion of the first oxygen-enriched gas stream into a second nitrogen gas in an upper portion of the second fractionator and a second oxygen-enriched liquefied fluid in a bottom portion of the second fractionator;
a second condenser for indirectly exchanging heat between the second nitrogen gas and the second oxygen-enriched liquefied fluid to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen and at the same time evaporating and gasifying the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid;
an expansion turbine into which a portion of the first oxygen-enriched gas stream is introduced;
a first product recovery path for outputting a portion of the first nitrogen gas as a first product nitrogen gas after heat recovery;
a second product recovery path for outputting a portion of the second nitrogen gas as a second product nitrogen gas after heat recovery;
a first liquefied nitrogen outlet path for extracting at least a portion of the first liquefied nitrogen and introducing it into a liquefied nitrogen storage tank;
A liquefied nitrogen injection passage for introducing liquefied nitrogen from the liquefied nitrogen storage tank into the second rectification column,
a liquid collection operation for extracting at least a portion of the first liquefied nitrogen from the first liquefied nitrogen discharge path;
a liquid injection operation in which liquefied nitrogen is introduced from the liquefied nitrogen storage tank into the second rectification column and the operation of the expansion turbine is stopped;
The above steps are repeated alternately. The method for operating a nitrogen production system according to claim 1, characterized in that the amount of feed air introduced into the first fractionator during the liquid injection operation is less than the amount of feed air introduced into the first fractionator during the liquid collection operation. The method for operating a nitrogen production system according to claim 1 or 2, characterized in that the amount of the second product nitrogen gas during the liquid injection operation is greater than the amount of the second product nitrogen gas during the liquid collection operation.

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