Operating method of nitrogen production apparatus

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

Technical Field

[0001] The present invention relates to an operation method of a nitrogen production apparatus, and more particularly, to an operation method of a nitrogen production apparatus that separates and purifies raw air by a cryogenic liquefaction separation method to collect product nitrogen (nitrogen gas, liquid nitrogen).

Background Art

[0002] For industrial production of nitrogen, a method of liquefying and separating air by a cryogenic liquefaction separation method is often adopted. As a method of industrially producing nitrogen using such a cryogenic liquefaction separation method, a nitrogen production method adopting a two-column nitrogen production apparatus process is disclosed (see, for example, Patent Document 1 and Patent Document 2).

[0003] The nitrogen production methods disclosed in Patent Document 1 and Patent Document 2 use a two-column nitrogen production apparatus equipped with two rectification columns, and in the single-column nitrogen production apparatus process using a single-column nitrogen production apparatus equipped with only one rectification column, (one of) the waste gas discharged from the rectification column was discarded. By introducing the waste gas from one rectification column as the raw material of the other rectification column, it is possible to significantly improve the product yield and the power consumption per unit.

[0004] FIG. 1 is a system diagram showing an example of the apparatus configuration of a so-called two-column nitrogen production apparatus equipped with two rectification columns, which is also used in Patent Document 1. Using this figure, a conventional basic operation method will be described.

[0005] First, in this nitrogen production apparatus, raw material air is pressurized to a predetermined pressure by a raw material air compressor 3, purified by a pretreatment adsorber 4, and then cooled by a main heat exchanger 6 in a cold insulation outer tank 5, and is subjected to low-temperature distillation to separate into a first nitrogen gas at the upper part of the column and a first oxygen-enriched liquefied fluid at the bottom of the column. There is a first rectification column 8, and the first nitrogen gas and the first oxygen-enriched liquefied fluid depressurized by a pressure reducing valve 16 are indirectly heat-exchanged to condense and liquefy the first nitrogen gas to obtain first liquefied nitrogen, and at the same time, the first oxygen-enriched liquefied fluid is evaporated and gasified to obtain a first oxygen-enriched gas fluid. There is a first condenser 13, and a part of the first oxygen-enriched gas fluid is subjected to low-temperature distillation to be rectification-separated into a second nitrogen gas at the upper part of the column and a second oxygen-enriched liquefied fluid at the bottom of the column. There is a second rectification column 51, and the second nitrogen gas and the second oxygen-enriched liquefied fluid depressurized by a pressure reducing valve 63 are indirectly heat-exchanged to condense and liquefy the second nitrogen gas to obtain second liquefied nitrogen, and at the same time, the second oxygen-enriched liquefied fluid is evaporated and gasified to obtain a second oxygen-enriched gas fluid. There is a second condenser 58, a first product recovery path 11 that leads out a part of the first nitrogen gas as a first product nitrogen gas after heat recovery, a second product recovery path 56 that leads out a part of the second nitrogen gas as a second product nitrogen gas after heat recovery, a first oxygen-enriched liquefied fluid confluence path 61 that connects the lower part of the first rectification column 8 and the lower part of the second rectification column 51 via a valve 62, an expansion turbine 24 that adiabatically expands a part of the first oxygen-enriched gas fluid, and a nitrogen compressor 54 that compresses the second product nitrogen gas.

[0006] Also, this nitrogen production apparatus is provided with liquefied nitrogen injection paths 71, 72 that introduce liquefied nitrogen stored in a liquefied nitrogen storage tank 80 into the first rectification column 8 and the second rectification column 51.

[0007] Next, the basic operation of this apparatus will be described. First, the raw material air taken in from path 1 through a filter 2 is compressed to a predetermined pressure by a raw material air compressor 3, and after impurities such as moisture and carbon dioxide are removed and purified by a pretreatment adsorber 4, it exchanges heat with product nitrogen gas and waste gas in a main heat exchanger 6 in a cold insulation outer tank 5 and is cooled to a predetermined temperature.

[0008] The raw air after compression, purification, and cooling is introduced from the main heat exchanger 6 through the raw air inlet path 7 to the lower part of the first rectification column 8, and is separated into the first nitrogen gas at the upper part of the column and the first oxygen-enriched liquefied fluid at the bottom of the column by cryogenic distillation using the cryogenic liquefaction separation method in the first rectification column 8.

[0009] In the first rectification column 8, the raw air after compression, purification, and cooling is introduced from the raw air inlet path 7 to the lower part of the column, and is separated into the first nitrogen gas at the upper part of the column and the first oxygen-enriched liquefied fluid at the bottom of the column by cryogenic distillation using the cryogenic liquefaction separation method in this first rectification column 8.

[0010] The first nitrogen gas extracted from the upper part of the column to the path 9 is partially branched to the path 10 to exchange heat with the raw air in the main heat exchanger 6, and after heat recovery, it is led out as the first product nitrogen gas from the first product recovery path 11. Also, the remaining first nitrogen gas is introduced into the first condenser 13 through the path 12.

[0011] The first oxygen-enriched liquefied fluid extracted from the lower part of the first rectification column 8 and depressurized to a predetermined pressure by the pressure reducing valve 16 is introduced into this first condenser 13 from the path 17. The first oxygen-enriched liquefied fluid and the first nitrogen gas perform indirect heat exchange. At the same time that the first nitrogen gas condenses and liquefies into the first liquefied nitrogen, the first oxygen-enriched liquefied fluid evaporates and gasifies into the first oxygen-enriched gas fluid. The first liquefied nitrogen is introduced into the upper part of the first rectification column 8 through the path 14 to become the reflux liquid.

[0012] On the other hand, the first oxygen-enriched gas fluid led out from the first condenser 13 to the path 18 is partially branched to the path 50 leading to the second rectification column 51, and then a very small part of the remainder is depressurized by the valve 19 and branched to the path 20, exchanges heat with the raw air in the main heat exchanger 6 for heat recovery, and is led out as waste gas from the waste gas lead-out path 21.

[0013] In addition, the first oxygen-enriched gas fluid that did not branch into path 50 and path 20 is introduced into the main heat exchanger 6 through path 22, heated to an intermediate temperature and then withdrawn through path 23, flows into the expansion turbine 24 and undergoes adiabatic expansion to generate the cold required for the operation of 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 led out as waste gas from the waste gas outlet path 21.

[0014] The first oxygen-enriched gas fluid introduced from path 50 to the lower part of the second rectification column 51 is separated, by means of low-temperature distillation within this second rectification column 51, into a second nitrogen gas at the upper part of the column and a second oxygen-enriched liquefied fluid at the bottom of the column. The second nitrogen gas withdrawn from the upper part of the column through path 52, a part of which branches into path 53 and exchanges heat with the raw material air in the main heat exchanger 6. After heat recovery, it is compressed to a predetermined pressure by the nitrogen compressor 54 and led out as a second product nitrogen gas from the second product recovery path 56. Also, the remaining second nitrogen gas is introduced into the second condenser 58 through path 57.

[0015] In this second condenser 58, the second oxygen-enriched liquefied fluid withdrawn from the lower part of the second rectification column 51 and the first oxygen-enriched liquefied fluid that branches into the first oxygen-enriched liquefied fluid confluence path 61 after being withdrawn from the lower part of the first rectification column 8 merge. After that, it is depressurized by the pressure reducing valve 63 and introduced from path 64 at a predetermined temperature. The second oxygen-enriched liquefied fluid after confluence and the second nitrogen gas perform indirect heat exchange, and the second nitrogen gas condenses and liquefies into second liquefied nitrogen. At the same time, the second oxygen-enriched liquefied fluid evaporates and gasifies into a second oxygen-enriched gas fluid. The second liquefied nitrogen is introduced into the upper part of the second rectification column 51 through path 59 and becomes a reflux liquid.

[0016] On the other hand, the second oxygen-enriched gas fluid led out from the second condenser 58 through path 65 is depressurized by the valve 66 and then merges into path 20. After exchanging heat with the raw material air in the main heat exchanger 6 for heat recovery, it is led out as waste gas from the waste gas outlet path 21.

[0017] The first product recovery path 11 and the second product recovery path 56 merge into a single path as path 70 on the downstream side, and the first product nitrogen gas and the second product nitrogen gas are derived.

[0018] The above is the configuration of the two-column nitrogen production apparatus and its basic operation method. However, in the operation method of FIG. 1 (Patent Document 1), further, according to the operating state of the apparatus and the required cooling capacity, the liquefied nitrogen stored in the liquefied nitrogen storage tank 80 is introduced into the first rectification column 8 and the second rectification column 51, so that it can be used as a cooling source required for the operation of each rectification column.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0020] However, for nitrogen production apparatuses that industrially produce nitrogen using the cryogenic liquefaction separation method, since a large amount of power is consumed, further reduction in unitization is required.

[0021] Therefore, in view of such demands, an object of the present invention is to provide an operation method for a nitrogen production apparatus capable of further reducing the consumed power and further reducing the power consumption unit.

Means for Solving the Problems

[0022] To achieve the above object, the operation method of the nitrogen production apparatus of the present invention is to use compressed, purified, and cooled raw material air by cryogenic liquefaction separation method Cryogenic distillation byA first fractionator separates the first nitrogen gas in the top of the column from a first oxygen-enriched liquefied fluid in the bottom of the column; a first condenser indirectly heat-exchanges the first nitrogen gas with 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; and by cryogenic liquefaction separation method Low temperature distillation by a second condenser that indirectly exchanges 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 evaporates and gasifies the second oxygen-enriched liquefied fluid to obtain a second oxygen-enriched gas fluid; an expansion turbine to which a portion of the first oxygen-enriched gas fluid is introduced; a first product recovery path that recovers heat from a portion of the first nitrogen gas and then discharges the portion of the second nitrogen gas as a first product nitrogen gas; a second product recovery path that recovers heat from a portion of the second nitrogen gas and then discharges the portion of the second nitrogen gas as a second product nitrogen gas; 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 column, and introduce it into the said liquid nitrogen storage tank Liquid collection operation, the first one introduced into the said liquid nitrogen storage tank by the said liquid sampling operation and a liquid injection operation in which liquefied nitrogen is introduced into the second fractionator and the operation of the expansion turbine is stopped, which are alternately repeated.

[0024] Furthermore, in the method for operating a nitrogen production apparatus of the present invention, the amount of the second nitrogen gas product in the liquid injection operation is preferably greater than the amount of the second nitrogen gas product in the liquid collection operation. Effect of the Invention

[0025] According to the present invention, When the liquid sampling operation is the main one, Traditional Basic Luck turn and With roughly the same power liquefy Nitrogen can be collected become , When the liquid injection operation is the main one, Almost the same as the conventional basic operation product quantity can reduce power consumptionsince it becomes, the liquid sampling operation and alternately with liquid injection operation appropriately by repeating move it becomes possible to store the reduction in force or the difference in power consumption as liquid nitrogen.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0027] Hereinafter, with reference to FIGS. 2 and 3, a two-column nitrogen production apparatus which is an embodiment of the present invention and an operation method of the nitrogen production apparatus will be described. In the following description, components that are the same as those of the nitrogen production apparatus described in FIG. 1 and have the same functions are denoted by the same reference numerals, and detailed descriptions including the operation method are omitted.

[0028] The nitrogen production apparatus shown in FIGS. 2 and 3 is a nitrogen production apparatus that cryogenically liquefies and separates raw material air to collect product nitrogen, similar to FIG. 1, and is a so-called two-column nitrogen production apparatus equipped with two rectification columns. As a difference from the nitrogen production apparatus shown in FIG. 1, in the case of the apparatus of FIG. 1, a liquid nitrogen injection path 71 for introducing liquid nitrogen from the liquid nitrogen storage tank 80 into the first rectification column 8 is provided, but for the nitrogen production apparatus shown in the present embodiment, a first liquid nitrogen derivation path 15 for branching from the path 14 and introducing a part of the first liquid nitrogen into the liquid nitrogen storage tank 80 is provided.

[0029] In addition, a so-called two-column nitrogen production apparatus is composed of rectifying columns with different operating pressures. That is, since the first oxygen-enriched liquefied fluid collected from the lower part of the first rectifying column 8 is depressurized and vaporized to form a first oxygen-enriched gas fluid and introduced into the second rectifying column 51, the operating pressure of the second rectifying column 51 is lower than that of the first rectifying column 8.

[0030] The operating method of the nitrogen production apparatus in this exemplary embodiment is not the above-described basic operation, but controls each part to alternately repeat a liquid sampling operation and a liquid injection operation as described below. The liquid sampling operation and the liquid injection operation are alternately and appropriately switched to operate so as to reduce the average power consumption.

[0031] (Liquid sampling operation) First, with reference to FIG. 2, the liquid sampling operation of the present invention will be described. In the liquid sampling operation, unlike the above-described basic operation, the first liquefied nitrogen liquefied by the first condenser 13 is introduced into the upper part of the first rectifying column 8 through the path 14 and becomes a reflux liquid, but a part of it is extracted from the first liquefied nitrogen derivation path 15 and sent to the liquefied nitrogen storage tank 80. In addition, in the liquid sampling operation, since the first liquefied nitrogen is collected in addition to the first product nitrogen gas, when collecting the same first product nitrogen gas as in the basic operation, it is necessary to increase the amount of raw material air compared to the basic operation.

[0032] (Liquid injection operation) Next, with reference to FIG. 3, the liquid injection operation of the present invention will be described. In the liquid injection operation, unlike the above-described basic operation, the operation of the expansion turbine 24 is stopped, and instead, liquefied nitrogen is used 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 rectifying column 51 through the liquefied nitrogen injection path 72. As described above, since the first oxygen-enriched liquefied fluid collected from the lower part of the first rectifying column 8 is depressurized and vaporized to form a first oxygen-enriched gas fluid and introduced into the second rectifying column 51, the operating pressure of the second rectifying column 51 is lower than that of the first rectifying column 8. Therefore, the liquefied nitrogen sent from the first rectifying column 8 to the liquefied nitrogen storage tank 80 through the first liquefied nitrogen derivation path 15 can be introduced into the second rectifying column 51 from the liquefied nitrogen injection path 72 without using a liquid pump.

[0033] Also, during the liquid injection operation, since the expansion turbine 24 is stopped, the entire amount of the first oxygen-enriched gas fluid passes through the path 50 and is introduced into the second rectification column 51.

[0034] The amount of raw air introduced into the first rectification column 8 during the liquid injection operation is less than the amount of raw air introduced into the first rectification column 8 during the liquid sampling operation. Also, the amount of the second product nitrogen gas during the liquid injection operation is more than the amount of the second product nitrogen gas during the liquid sampling operation.

[0035] In the operation method of the nitrogen production apparatus according to the present embodiment, a liquid sampling operation of extracting at least a part of the first liquefied nitrogen from the first liquefied nitrogen extraction path, and at least a part of the first liquefied nitrogen extracted in the liquid sampling operation is injected from the liquefied nitrogen injection path 72 into the second rectification column 51, and a liquid injection operation of stopping the operation of the expansion turbine 24 are appropriately switched and repeatedly operated alternately.

Example

[0036] (When the liquid sampling operation is the main operation) Table 1 shows a comparison between the case where the basic operation is performed for 24 hours and the case where the liquid sampling operation, which performs the liquid sampling operation for 15 hours and the liquid injection operation for 9 hours in a day, is the main operation.

[0037]

Table 1

[0038] In the case where this liquid sampling operation is the main operation, the power is 655 kW, which is almost the same as the basic operation, but 888 Nm of liquefied nitrogen 3 can be collected. In the case where the liquid sampling operation is the main operation, liquid nitrogen can be collected at 0.4% of the air volume with almost the same power as the basic operation.

Example

[0039] (When the liquid injection operation is the main operation) Table 2 shows a comparison between the case of performing the basic operation for 24 hours and the case of mainly performing a liquid injection operation in which liquid collection operation is carried out for 10 hours and liquid injection operation is carried out for 14 hours in a day.

[0040]

Table 2

[0041] In the case of mainly performing this liquid injection operation, 952 Nm 3 will be injected for 1000 Nm 3 of liquefied nitrogen collected in the liquid collection operation. It can be seen that the total power is 635 kW, and the power can be reduced by 3% compared with 654 kW in the basic operation. In the case of mainly performing the liquid injection operation, the power can be reduced by 3% compared with the basic operation by almost recycling the produced liquid for injection.

[0042] Liquid injection operation When taking [[it]] as the main one, Is almost the same as the basic operation manufacture of The power can be reduced with almost the same product quantity, and in the liquid collection operation When taking [[it]] as the main one, Liquid nitrogen can be collected with almost the same power as the basic operation. Therefore, if the liquid collection operation and the liquid injection operation are appropriately switched to operate the device as in the embodiment, when industrially producing nitrogen using the cryogenic liquefaction separation method, further reduction of the power consumption of the device used and further reduction of the power consumption per unit are possible.

[0043] 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 derivation path 15 can be introduced into the second rectification column 51 from the liquefied nitrogen injection path 72 without using a liquid pump, so that the power required for liquid injection can be reduced. In the conventional single rectification column, when collecting liquefied nitrogen 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 for injecting liquefied nitrogen.

[0044] Also, in the liquid injection operation, since the expansion turbine 24 is stopped, the corresponding amount of the first oxygen-enriched gas fluid can be introduced into the second rectification column 51. Since the second rectification column 51 has a high relative volatility due to its low operating pressure and a high product yield, as the introduced oxygen-enriched gas fluid increases, more second product nitrogen gas can be collected. In the liquid injection operation, the feed air can be reduced compared to the case of collecting the same amount of product nitrogen gas as in the basic operation, and the feed air compressor 3 can be operated at a reduced load compared to the basic operation. On the other hand, the power of the nitrogen compressor 54 increases as the second product nitrogen gas increases. However, since the reduction in the power of the feed air compressor 3, which accounts for most of the plant power, has a greater impact, the average power of the entire plant can be reduced.

[0045] In addition, in the liquid collection operation, since liquid nitrogen is collected in addition to the product nitrogen gas, when collecting the same amount of product nitrogen gas as in the basic operation, it is necessary to increase the amount of feed air compared to the basic operation. Therefore, the power of the feed air compressor 3 increases and the power of the liquid collection operation becomes large, but the impact of the power increase can be offset by combining it with the liquid injection operation. Therefore, by appropriately switching between the liquid injection operation and the liquid collection operation, it is possible to collect liquid nitrogen with almost the same power as the basic operation, the same amount of product nitrogen gas, and more.

[0046] Also, by performing such a liquid collection operation, it becomes possible to store surplus power in the form of liquid nitrogen. That is, basically, the liquid collection operation is performed at night when the power demand is low and the electricity price is low to store liquid nitrogen, and the liquid injection operation that consumes the collected liquid nitrogen during the day can suppress the power cost.

[0047] In addition, the revised Energy Conservation Law implemented in April 2021 added the concept of "smoothing of electricity demand", and it is specified that measures contributing to the smoothing of electricity demand, such as energy conservation and shifting the time zone of electricity use, shall be taken uniformly across the country between 8:00 and 22:00 from July to September (summer) and from December to March (winter). Along with this, the utilization of demand response (a mechanism in which end-users themselves change their electricity consumption patterns from normal patterns in response to time-varying electricity prices or rewards designed to reduce electricity use during times of high wholesale electricity prices or supply-demand tightness) is expected. By performing liquid collection / liquid injection operations as in this embodiment, further reduction of electricity charges can be achieved through the introduction of demand response, and it can also contribute to the stabilization of the power grid.

[0048] Note that the nitrogen production apparatus shown in this embodiment is an example, and each drawing does not necessarily reflect all the configurations of the nitrogen production apparatus. Furthermore, regarding the operation method, not only can the liquid collection operation and the liquid injection operation be repeated, but they can also be combined with basic operations, etc. as appropriate.

Explanation of Reference Numerals

[0049] 1... path, 2... filter, 3... raw air compressor, 4... pretreatment adsorber, 6... main heat exchanger, 8... first rectification column, 11... first product recovery path, 13... first condenser, 15... first product liquefied nitrogen derivation path, 16... pressure reducing valve, 21... waste gas derivation path, 24 expansion turbine, 51... second rectification column, 54... nitrogen compressor, 56... second product recovery path, 58... second condenser, 61... first oxygen-enriched liquefied fluid confluence path, 63... pressure reducing valve, 72... liquefied nitrogen injection path, 80... liquefied nitrogen storage tank

Claims

1. a first fractionator for separating the compressed, purified and cooled feed air by cryogenic distillation using a cryogenic liquefaction separation method into a first nitrogen gas at an upper part of the fractionator and a first oxygen-enriched liquefied fluid at a bottom part of the fractionator; a first condenser that indirectly exchanges heat 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 evaporate and gasify the first oxygen-enriched liquefied fluid to obtain a first oxygen-enriched gas fluid; a second fractionator for separating at least a portion of the first oxygen-enriched gas stream by cryogenic distillation using a cryogenic liquefaction separation method into a second nitrogen gas at an upper portion of the column and a second oxygen-enriched liquefied fluid at a bottom portion of the column; a second condenser that indirectly exchanges 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 simultaneously evaporate and gasify 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, comprising: a liquid collection operation in which at least a portion of the first liquefied nitrogen is extracted from the first liquefied nitrogen outlet path and introduced into the liquefied nitrogen storage tank; a liquid injection operation in which the first liquefied nitrogen introduced into the liquefied nitrogen storage tank by the liquid collection operation is introduced into the second rectification column and the operation of the expansion turbine is stopped; The above steps are repeated alternately.

2. 2. The method for operating a nitrogen producing apparatus according to claim 1, wherein the amount of the second nitrogen gas product in the liquid injection operation is greater than the amount of the second nitrogen gas product in the liquid extraction operation.

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