PACKING COLUMN

Description

[Technical Field]

[0001] The present invention relates to a packed column and relates in particular to a packed column suitable for distillation operations in cryogenic air separation unit.[Background Art]

[0002] FIG. 15 is a system diagram illustrating the basic configuration not according to the current invention of a nitrogen generator that distills from air as a raw material through cryogenic separation. This nitrogen generator 100 includes a distillation column 101 in which an upper liquid distributor 102, an upper gas-liquid contactor 103, an intermediate liquid distributor 104, and a lower gas-liquid contactor 105 are disposed in this order from the top. The upper gas-liquid contactor 103 and the lower gas-liquid contactor 105 are typically contactors using structured packing.

[0003] In a case of using this nitrogen generator 100 to distill nitrogen gas of 700 kPaG (gauge pressure; the same applies below) as a product, air as a raw material is compressed by an air compressor 106 to 760 kPaG. The heat of compression generated by the compression of the air is removed by an aftercooler 107, so that the compressed air is cooled to 40°C. Then, the carbon dioxide, water, and hydrocarbons contained in the air are removed through adsorption by a pre-treatment unit 108 that alternately uses two adsorbers, so that the air becomes purified air.

[0004] The purified air after exiting the pre-treatment unit 108 is introduced into a cold box 110 through a purified air stream 109 and cooled to -165°C, which is near the dew point, by a main heat exchanger 111. The cooled purified air is then introduced into a lower portion of the distillation column 101 through a gas introduction stream 112 as ascending gas in the distillation column 101. Nitrogen gas in an upper portion of the distillation column 101 separated by distillation operations inside the column is drawn to a gas discharge stream 113 at the top of the column. Part of the nitrogen gas branches off into a condensation stream 114 and is introduced into a condenser 115.

[0005] Meanwhile, at the bottom of the distillation column 101, oxygen-enriched liquid air is separated by the distillation, drawn into a liquid discharge stream 116, and lowered in pressure to 300 kPaG by a liquid-air pressure reducing valve 117, so that the temperature drops to -180°C due to the Joule-Thomson effect. This low-temperature liquid air is introduced into the condenser 115 and exchanges heat with the above-mentioned nitrogen gas. Consequently, the nitrogen gas is liquefied and the whole low-temperature liquid air is vaporized into low-temperature air. The liquid nitrogen liquefied at the condenser 115 is introduced into the upper portion of the distillation column 101 through a liquid introduction stream 118 as descending liquid in the distillation column 101.

[0006] The low-temperature air vaporized at the condenser 115 is introduced into the main heat exchanger 111 through a low-temperature air stream 119, exchanges heat with the purified air to be heated to -140°C, and is drawn in this intermediate temperature state into a turbine inlet stream 120 from an intermediate portion of the main heat exchanger 111. The low-temperature air in the intermediate temperature state is introduced into an expansion turbine 121, in which the low-temperature air is expanded to 30 kPaG and its temperature is lowered to -170°C by adiabatic expansion. The low-temperature air lowered in temperature by the expansion turbine 121 is introduced into the main heat exchanger 111 again through a turbine outlet stream 122 and exchanges heat with the purified air to cool the purified air. Consequently, the low-temperature air is sufficiently warmed to a temperature that is several °C lower than the purified air, and then discharged from the cold box 110 through a waste gas stream 123.

[0007] Also, the remaining portion of the nitrogen gas discharged into the gas discharge stream 113 from the distillation column 101 is introduced into the main heat exchanger 111. Then, as in the low-temperature air, the remaining portion of the nitrogen gas exchanges heat with the purified air to be sufficiently warmed to a temperature several °C lower than the purified air. Thereafter, the remaining portion of the nitrogen gas is discharged from the cold box 110 through a product nitrogen gas stream 124 and collected as a product nitrogen gas. In the case of distilling a product nitrogen gas at a pressure of 700 kPaG as described above, the distillation column 101 is operated at a high pressure of 730 kPaG.

[0008] In the distillation column 101, the liquid nitrogen introduced into the distillation column 101 from the condenser 115 through the liquid introduction stream 118 is distributed uniformly in the cross-sectional direction of the packed column 101 by the upper liquid distributor 102 and then flows down toward the upper gas-liquid contactor 103. The descending liquid flowing down from the lower end of the upper gas-liquid contactor 103 is distributed uniformly in the cross-sectional direction of the packed column 101 again by the intermediate liquid distributor 104 and then flows down toward the lower gas-liquid contactor 105. This is done so that the flow rate and composition of the descending liquid flowing down inside the upper gas-liquid contactor 103 and the lower gas-liquid contactor 105 while being in gas-liquid contact with the ascending gas, can be uniform.

[0009] Meanwhile, a configuration like a distillation column 131 illustrated in FIG. 16 is sometimes adopted in which a single liquid distributor 133 is disposed above a single gas-liquid contactor 132. However, widely used is a packed column 139 in which a gas-liquid contactor is divided vertically into a plurality of parts, for example, divided vertically into two gas-liquid contactors 135, 136, and an upper liquid distributor 137 and a intermediate liquid distributor 138 are provided respectively above the gas-liquid contactors 135, 136, as illustrated in FIG. 17 (see Patent Literature 1, for example). JP 2000 249464 A shows a gas-liquid contact device which brings liquid and gas into contact with each other while letting liquid flow down along the surface of a filler and besides raising gas, non-distribution-acceleration type of regular fillers and where thin plates or pipes in each shape to decide the direction of the stream of liquid or gas are stacked or disposed in vertical direction are used, and also this device is equipped with one piece each of liquid distributors and consisting of rough distribution parts and which roughly distribute liquid and fine distribution parts and which finely and equally distribute the liquid. JP H07 91825 A shows a a packed column according to the preamble of claim 1 into which lliquid is introduced through a liquid inlet nozzle at the top of the tower, then, is introduced into a gas / liquid contacting structural filler from a liquid dispersing device through liquid / gas dispersing structural filler. In this case, the liquid, dispersed uniformly by the filler, is brought into contact with gas phase, ascended from lower part, on the wall surface of the filler whereby the liquid is fractionated while accompanying material transfer. Biased flow of descending liquid is generated during passing layer divisions filled with the filler and the descending amount is reduced. Therefore, the descending liquid is introduced again into the liquid / gas dispersing structural filler. On the other hand, gas is introduced into the tower through gas inlet nozzle at the bottom of the tower, then, the gas is dispersed uniformly the filler and, thereafter, is contacted with the descending liquid by the filler.[Citation List][Patent Literature]

[0010] [Patent Literature 1] Japanese Patent Application No. 2000-337766[Summary of Invention][Technical Problems]

[0011] In a packed column operated at relatively low pressure, such as a packed column operated at 10 to 50 kPaG like a crude argon column in a cryogenic air separation unit, the relative volatility is 1.4 to 1.5, which is relative low, and the operating line and the equilibrium line in distillation is close to each other. It is therefore known that if small liquid maldistribution occurs, the operating line and the equilibrium line get closer to each other, thereby deteriorating the distillation performance (separation performance). To prevent maldistribution of the descending liquid, intermediate liquid distributors are placed at regular intervals, as illustrated in FIG. 17.

[0012] On the other hand, in a packed column operated at relatively high pressure, such as the one in the above-described nitrogen generator, the operating line and the equilibrium line are relatively far from each other in distillation in which the relative volatility is 1.9 to 3.1, that is, the operation pressure is 200 to 1500 kPaG. Thus, the direct influence of liquid maldistribution on deterioration in distillation performance is small. Despite that, there are cases where the distillation performance is still deteriorated when the packed column is used, even with intermediate liquid distributors placed therein.

[0013] No adequate solution to this problem has been developed. Currently, the problem is handled by simply increasing the height of the gas-liquid contactors in the packed column or increasing the amount of feed air. However, increasing the amount of the feed air results in increased power consumption at the air compressor. Also, increasing the height of the gas-liquid contactors increases not only the size of the distillation column but also the size of the cold box, which leads to a problem of an increased apparatus cost.

[0014] These problems occur not only with nitrogen generator but also with the high-pressure column (lower column) of cryogenic air separation unit by a double column system, which additionally generate oxygen and argon.

[0015] In view of this, an object of the present invention is to provide a packed column that is operated at relatively high pressure and prevent deterioration in distillation performance without having to increase the height of its gas-liquid contactors or increase the amount of air.[Solution to Problems]

[0016] The above object is achieved by the subject matter of the independent claim.

[0017] The packed column of the present invention is characterized in that a total height of the gas-liquid contactors above the highest gas disperser of the two or more gas dispersers is set such that a ratio of the total height to a height of all the gas-liquid contactors is 0.5 or greater.

[0018] Also, the packed column of the present invention may further comprise at least one intermediate liquid distributor that distributes the descending liquid again.

[0019] In addition, one of the gas dispersers may be formed integrally with the intermediate liquid distributor.[Advantageous Effect(s) of Invention]

[0020] According to the packed column of the present invention, the ascending gas rising toward a gas-liquid contactor can be dispersed by the respective of the two or more gas dispersers. In this way, the composition of the ascending gas can be uniformed, and the flow rate of the ascending gas can be uniformed as well. Thus, decrease in distillation efficiency and gas-liquid contact efficiency can be suppressed. It is therefore possible to reduce the height of the gas-liquid contactors and reduce the amount of gas and liquid to be introduced.[Brief Description of Drawings]

[0021] [FIG. 1] FIG. 1 is an explanatory diagram illustrating a first example of a packed column not according to the present invention. [FIG. 2] FIG. 2 is a schematic cross-sectional view illustrating an example of a gas disperser. [FIG. 3] FIG. 3 is a schematic bottom view of the same. [FIG. 4] FIG. 4 is an explanatory diagram illustrating a second example of a packed column not according to the present invention. [FIG. 5] FIG. 5 is a simulation model corresponding to the first example. [FIG. 6] FIG. 6 is a simulation model of a conventional example provided with no gas disperser or intermediate liquid distributor. [FIG. 7] FIG. 7 is a graph illustrating the correlations between the liquid maldistribution rate and the performance deterioration rate obtained from the simulation models of FIGS. 5 and 6. [FIG. 8] FIG. 8 is a simulation model corresponding to the second example. [FIG. 9] FIG. 9 is a simulation model corresponding to a packed column in which an intermediate liquid distributor is placed between an upper gas-liquid contactor and a lower gas-liquid contactor. [FIG. 10] FIG. 10 is a graph illustrating the correlations between the liquid maldistribution rate and the performance deterioration rate obtained from the simulation models of FIGS. 8 and 9. [FIG. 11] FIG. 11 is a graph illustrating the correlations between the operation pressure and the performance deterioration rate obtained from the simulation models of FIGS. 8 and 9. [FIG. 12] FIG. 12 is a graph illustrating the correlation between the performance deterioration rate and the ratio of the total height of each upper gas-liquid contactor model and each intermediate gas-liquid contactor model to the entire height of all gas-liquid contactor models obtained from the simulation model of FIG. 8. [FIG. 13] FIG. 13 is a graph illustrating the correlation between the performance deterioration rate and the ratio of the total height of each upper gas-liquid contactor model and each intermediate gas-liquid contactor model to the height of all gas-liquid contactor models obtained from the simulation model of FIG. 5. [FIG. 14] FIG. 14 is a simulation model in which an intermediate liquid distributor and a gas disperser are provided between upper gas-liquid contactors and lower gas-liquid contactors. [FIG. 15] FIG. 15 is a system diagram illustrating the basic configuration of a nitrogen generator. [FIG. 16] FIG. 16 is an explanatory diagram illustrating an example of a distillation column in which a single liquid distributor is disposed above a single gas-liquid contactor. [FIG. 17] FIG. 17 is an explanatory diagram illustrating an example of a packed column in which an upper liquid distributor and an intermediate liquid distributor are provided respectively above vertically divided two gas-liquid contactors. [Description of Examples]

[0022] FIG. 1 illustrates a first example of a packed column. This packed column 11 is a packed column with a gas-liquid contactor provided inside a tubular body 16 including a gas introduction portion 12 and a liquid discharge portion 13 at the bottom and including a gas discharge portion 14 and a liquid introduction portion 15 at the top. The gas-liquid contactor in the tubular body 16 is formed into vertically divided upper gas-liquid contactor 17 and lower gas-liquid contactor 18. Above the upper gas-liquid contactor 17, a liquid distributor 19 is provided which causes liquid introduced from the liquid introduction portion 15 to flow down uniformly toward the upper gas-liquid contactor 17. Between the upper gas-liquid contactor 17 and the lower gas-liquid contactor 18, a gas disperser 20 is provided which uniformly disperses the composition of ascending gas rising from the lower gas-liquid contactor 18 toward the upper gas-liquid contactor 17.

[0023] The ascending gas introduced from the gas introduction portion 12 is subjected to a distillation operation in the lower gas-liquid contactor 18, introduced into the gas disperser 20 to be dispersed, introduced into the upper gas-liquid contactor 17 to be subjected to a distillation operation, and then discharged from the gas discharge portion 14. On the other hand, the descending liquid introduced from the liquid introduction portion 15 is distributed by the liquid distributor 19 and introduced into the upper gas-liquid contactor 17 and the lower gas-liquid contactor 18 in this order. The liquid thus introduced becomes maldistributed as it descends, and is discharged from the liquid discharge portion 13.

[0024] FIG. 2 is a schematic cross-sectional view illustrating an example of the gas disperser 20, and FIG. 3 is a schematic bottom view of the same. In this gas disperser 20, the ascending gas rising from the lower gas-liquid contactor 18 passes through a plurality of paths 21 and resisted by turn back portions 22, so that its composition becomes even horizontally. The ascending gas flowing from the gas disperser 20 into the upper gas-liquid contactor 17 is introduced thereinto such that its flow rate has a distribution dependant on the maldistribution of the descending liquid flowing down in the upper gas-liquid contactor 17. Also, the descending liquid flowing down out of the upper gas-liquid contactor 17 flows down into liquid receiving portions 23 from the upper sides of the turn back portions 22 and then flows down through bottom holes 24 toward the lower gas-liquid contactor 18.

[0025] FIG. 4 illustrates a second example of a packed column. Note that in the following description, identical constituent elements to the constituent elements of the packed column presented in the first example will be denoted by the identical reference signs, and detailed description thereof will be omitted.

[0026] In this packed column 31, a gas-liquid contactor in a tubular body 32 is formed into three horizontally divided upper gas-liquid contactor 33a, intermediate gas-liquid contactor 33b, and lower gas-liquid contactor 34. An upper liquid distributor 35a is provided above the upper gas-liquid contactor 33a, an intermediate liquid distributor 35b is provided between the upper gas-liquid contactor 33a and the intermediate gas-liquid contactor 33b, and a gas disperser 36 is provided between the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor 34.

[0027] Ascending gas introduced into a lower portion of the packed column 31 from the gas introduction portion 12 is subjected to a distillation operation in the lower gas-liquid contactor 34, introduced into the gas disperser 36 to be dispersed, introduced into the intermediate gas-liquid contactor 33b and the upper gas-liquid contactor 33a in this order to be subjected to distillation operations, and then discharged from the gas discharge portion 14. On the other hand, descending liquid introduced from the liquid introduction portion 15 is distributed in the upper liquid distributor 35a, introduced into the upper gas-liquid contactor 33a, and then distributed again in the intermediate liquid distributor 35b. Thereafter, the descending liquid is introduced into the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor 34 in this order to be subjected to distillation operations.

[0028] The results of simulations performed to check the effect of placing a gas disperser between upper and lower gas-liquid contactors will be described below. Meanwhile, in each simulation model, descending liquid is indicated by solid lines while ascending gas is indicated by broken lines.

[0029] FIG. 5 is a simulation model of the case where the gas disperser 20 is provided between the upper gas-liquid contactor 17 and the lower gas-liquid contactor 18, as illustrated in the first example. Descending liquid to be introduced into packed column models 41, 42 is introduced at a given ratio from a liquid distributor model 43 into the uppermost portions of the packed columns, and then reaches the lowermost portions of the packed column models 41, 42. Also, assuming that the total amount of descending liquid to be introduced into the packed column models 41, 42 is LF and the amount by which the amount of descending liquid is to be adjusted by the liquid distributor model 43 is δF, an amount LF1 of descending liquid to be introduced into the first packed column model 41 is LF / 2 + δF while an amount LF2 of descending liquid to be introduced into the second packed column model 42 is LF / 2 - δF, and δF / LF is the liquid maldistribution rate.

[0030] In this simulation model, a gas disperser model 46 corresponding to the gas disperser 20 is provided between upper gas-liquid contactor models 44 and lower gas-liquid contactor models 45. FIG. 6 is a simulation model of a conventional example provided with no gas disperser or intermediate liquid distributor, as illustrated in FIG. 16.

[0031] In the simulation model illustrated in FIG. 5, feed air to be introduced from a gas introduction portion 47 is introduced into the packed column models 41, 42 as ascending gases and subjected to distillation operations in the respective lower gas-liquid contactor models 45. Thereafter, the ascending gases are introduced into the gas disperser model 46 to uniform the compositions of the ascending gases, introduced into the respective upper gas-liquid contactor models 44 to be subjected to distillation operations, and then rise to the uppermost portions of the respective packed column models 41, 42.

[0032] The descending liquid to be introduced from a liquid introduction portion 48 is introduced at a given ratio from the liquid distributor model 43, and then descends to the lowermost portions of the respective packed column models without their flow rates or compositions corrected at the intermediate portions.

[0033] In the simulation model illustrated in FIG. 6, feed air to be introduced from a gas introduction portion 51 is introduced into packed column models 52, 53 as ascending gases and then introduced from lower gas-liquid contactor models 54 directly into upper gas-liquid contactor models 55. These ascending gases rise to the uppermost portions of the respective packed column models 52, 53 without their flow rates or compositions corrected. Descending liquid to be introduced from a liquid introduction portion 56 is introduced at a given ratio from a liquid distributor model 57 into the uppermost portions of the packed column models 52, 53, and then descend to the lowermost portions of the respective packed column models 52, 53 without their flow rates or compositions corrected, as in the simulation model illustrated in FIG. 5.

[0034] FIG. 7 illustrates the result of calculation of the performance deterioration rate versus the liquid maldistribution rate (δF / LF) using each of the simulation models illustrated in FIGS. 5 and 6. A performance deterioration rate 6A of the conventional example model illustrated in FIG. 6 sharply increases after a liquid maldistribution rate of 1%. This is because the compositions of the ascending gases in the packed column model 52, 53 become markedly different from each other. On the other hand, a performance deterioration rate 5A of the first example model illustrated in FIG. 5, in which the gas disperser model 46 is placed to uniform the composition of the ascending gas, changes gently up to a liquid maldistribution rate of 5%, and performance deterioration hardly occurs up to a liquid maldistribution rate of 2%. This result indicates that placing a gas disperser to uniform the composition of the ascending gas can effectively suppress performance deterioration.

[0035] FIG. 8 is a simulation model of the case where a gas-liquid contactor is formed into the horizontally divided upper gas-liquid contactor 33a, intermediate gas-liquid contactor 33b, and lower gas-liquid contactor 34, the upper liquid distributor 35a is provided above the upper gas-liquid contactor 33a, the intermediate liquid distributor 35b is provided between the upper gas-liquid contactor 33a and the intermediate gas-liquid contactor 33b, and the gas disperser 36 is provided between the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor 34, as illustrated in the second example.

[0036] In this simulation model, feed air to be introduced from a gas introduction portion 61 is introduced into lower portions of packed column models 62, 63 as ascending gases and subjected to distillation operations in respective lower gas-liquid contactor models 64. Thereafter, the ascending gases are introduced into a gas disperser model 65 to uniform the compositions of the ascending gases, and rise through intermediate gas-liquid contactor models 66b and upper gas-liquid contactor models 66a to the uppermost portions of the respective packed column models 62, 63.

[0037] On the other hand, descending liquid to be introduced from a liquid introduction portion 67 is introduced at a given ratio from an upper liquid distributor model 68a into upper portions of the packed column models 62, 63, subjected to distillation operations in upper gas-liquid contactor models 66a, and have their compositions uniformed in an intermediate liquid distributor model 68b. Thereafter, the resultant descending liquid is introduced at the same ratio as that by the upper liquid distributor model 68a into the intermediate gas-liquid contactor models 66b, introduced directly into the lower gas-liquid contactors 64, and descend to the lowermost portions of the packed column models 62, 63.

[0038] FIG. 9 is a simulation model of the packed column 139, in which the intermediate liquid distributor 138 is placed between the horizontally divided two upper gas-liquid contactor 135 and lower gas-liquid contactor 136, as illustrated in the conventional example of FIG. 17.

[0039] In this simulation model, feed air to be introduced from a gas introduction portion 71 is introduced into packed column models 72, 73 as ascending gases and subjected to distillation operations in respective lower gas-liquid contactor models 74. Then, the ascending gases rise directly through upper gas-liquid contactor models 75 to the uppermost portions of the respective packed column models 72, 73 without their flow rates or compositions corrected.

[0040] On the other hand, descending liquid to be introduced from a liquid introduction portion 76 is introduced at a given ratio from an upper liquid distributor model 77 into the packed column models 72, 73, subjected to distillation operations in the upper gas-liquid contactor models 75, and have their compositions uniformed in an intermediate liquid distributor model 78. Then, the resultant descending liquid is introduced at the same ratio as that by the upper liquid distributor model 77 into the lower gas-liquid contactor models 74, and descends to the lowermost portions of the packed column models 72, 73.

[0041] FIG. 10 illustrates the result of calculation of the performance deterioration rate versus the liquid maldistribution rate using each of the simulation models illustrated in FIGS. 8 and 9. A performance deterioration rate 9A of the simulation model illustrated in FIG. 9, in which no gas disperser is placed but an intermediate liquid distributor is placed, changes gently with increase in liquid maldistribution rate. The performance deterioration rate 9A is effective to some extent in reducing the rate of deterioration in distillation performance as compared to the performance deterioration rate 6A of the conventional example model, illustrated in FIG. 7. Nonetheless, a performance deterioration rate 8A of the simulation model illustrated in FIG. 8 indicates that a higher suppressing effect can be achieved by using both an intermediate liquid distributor and a gas disperser.

[0042] Further, FIG. 11 illustrates the result of calculation of the performance deterioration rate versus the operation pressure using each of the simulation models illustrated in FIGS. 8 and 9 with the liquid maldistribution rate set to 3%. As for a performance deterioration rate 9B of the simulation model illustrated in FIG. 9, in which no gas disperser is placed, when the operation pressure is higher than or equal to 200 kPaG, the maldistribution of the ascending gases causes a great difference in composition between the ascending gases, and therefore the performance deterioration rate is markedly high. In contrast, a performance deterioration rate 8B of the simulation model illustrated in FIG. 8, in which a gas disperser is placed, indicates that the simulation model can suppress deterioration in distillation performance in the operation pressure range of 200 to 1500 kPaG, i.e., in the relative volatility range of 1.9 to 3.1.

[0043] Furthermore, FIG. 12 illustrates the result of consideration of the relationship between the position of placement of a gas disperser and the performance deterioration rate using the simulation model illustrated in FIG. 8. A performance deterioration rate 8C is calculated in a setting where in FIG. 8, the height of each upper gas-liquid contactor model 66a is H1A, the height of each intermediate gas-liquid contactor model 66b is H1B, the height of each lower gas-liquid contactor model 64 is H2, and the height H2 of the lower gas-liquid contactor model 64 is reduced while the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1A of the upper gas-liquid contactor model 66a are fixed, that is, the gas disperser 65 is shifted downward without changing the entire height. FIG. 12 illustrates the result.

[0044] This result indicates that the effect of suppressing performance deterioration is high when the ratio of the total height of the upper gas-liquid contactor model 66a and the intermediate gas-liquid contactor model 66b to the entire height of all gas-liquid contactor models is set to 0.5 or greater and in particular to 0.7 or greater. Note that although the performance deterioration rate is calculated in the setting where the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1A of the upper gas-liquid contactor model 66a are fixed, the advantageous effect of the invention of the present application can be achieved regardless of which part is fixed in length. For example, the performance deterioration rate may be calculated with the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1B of the intermediate gas-liquid contactor model 66b fixed.

[0045] Further, using the simulation model illustrated in FIG. 5, a performance deterioration rate 5A is calculated in a similar setting where the height of each upper gas-liquid contactor model 44 is H1, the height of each lower gas-liquid contactor model 45 is H2, and the height H2 of the lower gas-liquid contactor model 45 is reduced while the entire height of all gas-liquid contactor models (H1 + H2) is fixed, that is, the gas disperser 46 is shifted downward without changing the entire height of all gas-liquid contactor models. As illustrated in FIG. 13, this result also indicates that the effect of suppressing performance deterioration is high when the ratio of the height H1 of the upper gas-liquid contactor model 44 to the entire height of all gas-liquid contactors is set to 0.5 or greater and preferably to 0.7 or greater. Note that although the performance deterioration rate is calculated in the setting where the entire height of all gas-liquid contactor models (H1 + H2) is fixed, the advantageous effect of the invention of the present application can be achieved regardless of which part is fixed in length.

[0046] FIG. 14 is a simulation model in which an intermediate liquid distributor 83 and a gas disperser 84 are provided between upper gas-liquid contactors 81 and lower gas-liquid contactors 82. In the case of providing the intermediate liquid distributor 83 and the gas disperser 84 at the same position as above, a liquid distributor-gas disperser unit formed to integrate a liquid distributing function and a gas dispersing function can be provided. This result is illustrated by the black triangle in FIG. 12 (H1B is zero). The same result as the simulation model illustrated in FIG. 8 is obtained at the point where the ratio of (H1A + H1B) to (H1A + H1B + H2) is 0.7.

[0047] Note that each single gas-liquid contactor in the present invention refers to a portion including a gas-liquid contactor between an introduction portion or discharge portion for descending liquid and an introduction portion or discharge portion for ascending gas. The present invention is applicable to each gas-liquid contactor in a packed column including a plurality of gas-liquid introduction portions and gas-liquid discharge portions inside a tubular body. Moreover, the structure of the gas disperser may be any suitable structure.[Reference Signs List]

[0048] 11packed column 12gas introduction portion 13liquid discharge portion 14gas discharge portion 15liquid introduction portion 16tubular body 17upper gas-liquid contactor 18lower gas-liquid contactor 19liquid distributor 20gas disperser 21path 22turn back portion 23liquid receiving portion 24bottom hole 31packed column 32tubular body 33aupper gas-liquid contactor 33bintermediate gas-liquid contactor 34lower gas-liquid contactor 35aupper liquid distributor 35bintermediate liquid distributor 36gas disperser 41, 42packed column model 43liquid distributor model 44upper gas-liquid contactor model 45lower gas-liquid contactor model 46gas disperser model 47gas introduction portion 48liquid introduction portion 51gas introduction portion 52, 53packed column model 54lower gas-liquid contactor model 55upper gas-liquid contactor model 56liquid introduction portion 57liquid distributor model 61gas introduction portion 62, 63packed column model 64lower gas-liquid contactor model 65gas disperser model 66aupper gas-liquid contactor model 66bintermediate gas-liquid contactor model 67liquid introduction portion 68aupper liquid distributor model 68bintermediate liquid distributor model 71gas introduction portion 72, 73packed column model 74lower gas-liquid contactor model 75upper gas-liquid contactor model 76liquid introduction portion 77upper liquid distributor model 78intermediate liquid distributor model 81upper gas-liquid contactor 82lower gas-liquid contactor 83intermediate liquid distributor 84gas disperser 100nitrogen generator 101distillation column 102upper liquid distributor 103upper gas-liquid contactor 104intermediate liquid distributor 105lower gas-liquid contactor 106air compressor 107aftercooler 108pre-treatment unit 109purified air stream 110cold box 111main heat exchanger 112gas introduction stream 113gas discharge stream 114condensation stream 115condenser 116liquid discharge stream 117liquid-air pressure reducing valve 118liquid introduction stream 119low-temperature air stream 120turbine inlet stream 121expansion turbine 122turbine outlet stream 123waste gas stream 124product nitrogen gas stream 131distillation column 132gas-liquid contactor 133liquid distributor 135, 136gas-liquid contactor 137upper liquid distributor 138intermediate liquid distributor 139packed column

Claims

1. A packed column (11; 31) which includes a gas-liquid contactor (17, 18; 33a, 33b, 34) inside a tubular body (16; 32) and a liquid distributor (19; 35a) in an uppermost portion and causes descending liquid and ascending gas to contact each other in the gas-liquid contactor (17, 18; 33a, 33b, 34), wherein operation pressure is in a range of 200 to 1500 kPaG, relative volatility is in a range of 1.9 to 3.1, the gas-liquid contactor is horizontally divided into at least two parts to thereby form a plurality of gas-liquid contactors (17, 18; 33a, 33b, 34), wherein: two or more gas dispersers (20; 36) is-are each provided between a lower one (18; 34) of the gas-liquid contactors and an upper one (17; 33a) of the gas-liquid contactors, the gas dispersers (20) uniformly dispersing composition of the ascending gas rising from the respective lower gas-liquid contactor (18) toward the respective upper gas-liquid contactor (17), characterised in that a total height of the gas-liquid contactors (17; 33a, 33b) above the highest gas disperser (20; 36) of the two or more gas dispersers is set such that a ratio of the total height to a height of all the gas-liquid contactors (17, 18; 33a, 33b, 34) is 0.5 or greater, in particular 0.7 or greater.

2. The packed column (31) according to claim 1, characterized in that the packed column (31) further comprises at least one intermediate liquid distributor (35b) that distributes the descending liquid again.

3. The packed column (31) according to claim 2, characterized in that one of the gas dispersers (36) is formed integrally with the intermediate liquid distributor (35b).