JPH0735472A - Air separation device - Google Patents

Abstract

(57) [Abstract] [Purpose] As a rectification column used in an air separation device, in a rectification column in which packings having a regular structure are stacked in the tower, the liquid falling from above passes through the packings. It prevents the rectification efficiency from being lowered due to uneven flow. [Structure] The rectification column comprises a packing 1 having a regular structure,
A liquid dispersion device 2, a liquid collection device 3, a gas outlet nozzle 4,
Liquid inlet nozzle 5, gas inlet nozzle 6 and liquid outlet nozzle 7
Have and. The height 8 of the continuous packing in the rectification column was reduced to 0.
The range is limited to 5 m or more and 10 m or less, and the liquid collection device 3 and the liquid dispersion device 2 are installed between them. [Effect] The drift of the falling liquid can be prevented, and the performance of the packing can be effectively enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used as a rectification column of an air separation device for compressing, purifying, and cooling air and then introducing the air to a rectification column for deep-chill separation into oxygen, nitrogen, argon, and other gases. Rectifying column.

[0002]

2. Description of the Related Art In a conventional rectification column of an air separation device, perforated plate-shaped rectification trays are used as means for mass transfer by gas-liquid contact, and the rectification trays are stacked in a tray form at intervals of 100 to 200 mm. Mainly used was a tray type rectification tower. On the other hand, the packing type rectification column in which packing elements with an extremely small size compared to the inner diameter of the rectification column are randomly packed in the rectification column, and the outer diameter of the packing material is almost the same as the inner diameter of the rectification column. In addition, the use of a packed rectification column in which a packing having a regular structure and having a proper void in the packing is packed has also been studied for a long time. Examples of the former irregular packing include Raschig rings and bell saddles, and examples of the latter ordered packing include Steadman packing. Conventionally, a packed rectification column in which such irregular packing or ordered packing is packed in the column is not so effective as a rectification column of an air separation device because of its poor rectification efficiency as compared with a plate rectification column. It was not used.

On the other hand, the rectification efficiency is equal to or higher than that of the plate rectification column and the pressure loss is higher than that of the plate rectification column or the conventional packed rectification column packed with packings. A packed rectification column in which a regular packing having a new structure capable of remarkably lowering is packed in the column has been widely used mainly in the field of petrochemistry. By replacing the existing plate type rectification column with the rectification column filled with the packing of this new structure, the pressure loss per unit height is reduced, and as a result, the theoretical plate number in the rectification column is increased and the performance is improved. There are many reports that have improved the.

In recent years, in the field of air separation devices, packed type rectification columns, in which ordered packing having a new structure is filled in the rectification columns, have begun to be used, and as the pressure loss in the rectification column is reduced, the raw materials are reduced. Attempts have been made to reduce the discharge pressure of the air compressor and to improve the performance of the air separation device by increasing the theoretical number of stages.

In a packed rectification column, dispersion of liquid in the rectification column is very important. If the liquid that descends on the surface of the packing in the rectification column is unevenly distributed, the expected rectification efficiency improvement and pressure loss reduction effects cannot be obtained. In a rectification column that uses ordered packing that can significantly improve rectification performance compared to conventional packing, uniform liquid dispersion in the horizontal cross section of the rectification column is one of the important factors that affect rectification performance. It becomes one. It is well known in the field of petrochemicals and the like to install a liquid collector and a liquid disperser in order to achieve uniform liquid dispersion, and various structures of the liquid collector and the liquid disperser itself are used. A structure has been proposed.

However, since the physical properties of the air separation device are greatly different from those in the field of petrochemistry, whether or not the liquid collection device and the liquid dispersion device proposed so far in the field of petrochemistry are appropriate. Is not clear. In addition, there is no indication of how far apart the liquid collector and liquid disperser should be placed.

[0007]

As a rectification column of an air separation device, a high pressure column for introducing air to separate nitrogen and oxygen-rich components, a nitrogen-rich component and an oxygen-rich component are used. A low-pressure column that introduces and separates product nitrogen and product oxygen, a crude argon column that introduces oxygen slightly containing argon extracted from the middle part of the low-pressure column and separates it into argon-rich components, and other concentration columns A rectification column is used as. When a packed rectification column is used as the rectification column, the packing height of the ordered packing reaches a maximum of about 40 m.

The rectification in the rectification column is achieved by mass transfer due to gas-liquid contact between the descending liquid from above and the ascending gas from below, which have different compositions. In the case of a packed rectification column, the liquid falling from above flows down on the surface of the packing while forming a thin film on the surface of the packing, making countercurrent gas-liquid contact with the gas phase to prevent mass transfer as a wetting wall. The rectification separation is carried out by utilizing it. In order to improve the performance of the packing, it is necessary to provide a sufficient contact area between gas and liquid. It does not mean that the surface area per unit packed volume of the packing, ie the specific surface area, simply needs to be large. Even if there is a packing having a very large specific surface area, the liquid supply from above to the packing is not evenly distributed to the packing,
If a sufficient thin film cannot be formed on the entire surface of the packing, it is not useful for increasing the gas-liquid contact area, and the rectification effect cannot be expected.

In order to achieve uniform liquid dispersion, a liquid dispersion device is installed in the upper space where the packings are stacked. The liquid dispersion device initially enables uniform liquid dispersion in the packing. However, since the falling liquid cannot avoid unequal flow while passing through the packed bed, the effective gas-liquid contact area per unit volume gradually decreases, and the rectification efficiency decreases.

In recent years, the individual height of the ordered packing having a new structure which has begun to be used in the packed rectification column of the air separation device is about 200 mm. In the rectification column, individual ordered packings are continuously stacked in layers. In the case of the air separation device, if the continuous filling height of the ordered packing is 10 m, about 50 ordered packing will be continuously stacked. However, the higher the continuous filling height is, the larger the drift of the descending liquid from above becomes, so that the rectification efficiency per unit height further decreases.

In the present invention, regarding a packed type rectification column in which a regular packing used in an air separation device is packed in the column, uneven flow of the falling liquid passing through the packing in the horizontal section of the rectification column is suppressed, and the rectification efficiency is reduced. The purpose of this is to prevent the deterioration of the filling and to bring out the full performance of the filling material.

Another object of the present invention is to prevent a decrease in the dispersion efficiency of the falling liquid due to an increase in the height of the continuous packing material, which results in a decrease in the rectification efficiency of the packing material (that is, HET).
To increase P).

[0013]

In order to achieve the above object, the continuous packing height of the ordered packing in the packed rectification column is set within a limited range, for example, in the range of 0.5 m to 10 m. And install a liquid collection device and a liquid dispersion device between them.

[0014]

Even if a liquid collecting device and a dispersing device are installed below 0.5 m, the effects of these devices cannot be obtained. On the other hand, when the continuous filling height exceeds 10 m, HETP deteriorates rapidly. Therefore, if the packing height is in the range of 0.5 m to 10 m, the reduction of the rectification efficiency due to the drift of the falling liquid in the rectification column can be minimized.

[0015]

EXAMPLE FIG. 1 shows an example of the structure of a rectification column in which a regular packing is filled in the column. 1 is a packing having a regular structure, 2 is a liquid dispersion device, 3 is a liquid collection device, 4 is a gas outlet nozzle, 5 is a liquid inlet nozzle, 6 is a gas inlet nozzle, 7 is a liquid outlet nozzle, and 8 is It is the continuous filling height of a filling with a regular structure.

The gas feed is introduced into the tower through a gas inlet nozzle 6 installed at the bottom of the tower. The gas feed introduced into the column rises in the column due to the pressure difference in the column, and the regular packing 1 performs rectification by gas-liquid contact with the liquid phase,
Finally, it is taken out as a product gas from a gas outlet nozzle 4 installed at the top of the tower.

On the other hand, the liquid feed is introduced into the column through the liquid inlet nozzle 5 installed at the top of the column, and after passing through the liquid dispersion device 2, it is introduced into the ordered packing 1 due to the difference in gravity. The liquid dispersion device 2 is devised so that the liquid is uniformly dispersed in the horizontal section of the rectification column.
The liquid is evenly distributed on the upper end surface of the. The liquid distributed on the upper end surface of the ordered packing 1 forms a thin liquid film along the surface of the packing, and descends while being rectified by gas-liquid contact with the gas phase on the liquid film surface, Finally, it is collected in the liquid reservoir at the bottom of the tower and taken out of the tower as a product liquid by the liquid outlet nozzle 7. On the way, in order to correct the drift generated while the falling liquid is passing through the ordered packing, the falling liquid is once collected by the liquid collecting device 3 and then uniformly dispersed by the liquid dispersing device 2 again. It is continuously introduced into the ordered packing 1 installed in the.

The individual height of the ordered packing 1 is about 200 mm. In the rectification column, each packing is used by stacking several layers, and the height of the continuous packing is indicated by 8 in FIG. There is a difference in the degree of uneven flow of the liquid between the upper end surface and the lower end surface of the continuous packing.

In order to quantitatively evaluate the degree of drift of the descending liquid in the rectification column, the following defining equation is used.

[0020] Here, Wi: a flow rate per unit time which is obtained by decomposing a cross section perpendicular to the liquid and gas flow directions of the rectification tower into minute surfaces so that each area becomes equal, and passing through each minute surface.
The length of one side of the minute surface varies depending on the inner diameter of the rectification column, but is about 1 to 10 cm.

Wave: Average value of the flow rate per unit time passing through each minute surface per unit time.

N: number of divided minute faces, that is, it can be said that the closer the dispersion efficiency is to 100%, the more uniformly the liquid is dispersed in the cross section of the rectification column. On the other hand, it can be said that the lower the dispersion efficiency, the more the drift occurs.

As the continuous packing height of the ordered packing increases, the dispersion efficiency decreases, and the rectification efficiency per unit packing height decreases. In general, the rectification efficiency per unit filling height is expressed by the theoretical plate number per unit height (HETP). HE
It is understood that the smaller the TP, the smaller the packing height for achieving the rectification of one theoretical stage, and the better the rectification efficiency.

A simulation was conducted to investigate the degree of uneven flow generated when the falling liquid passed through the ordered packing, and the increase and decrease in the rectification efficiency. The simulation results are shown in FIGS. 2 and 3.

FIG. 2 shows the continuous filling height on the horizontal axis and the dispersion efficiency according to the above definition formula on the vertical axis, and shows how the dispersion efficiency decreases as the continuous filling height increases. According to FIG. 2, the dispersion efficiency is almost 100% at the filling height of 0.6 to 0.8 m or less, but it begins to drop when it exceeds about 1 m. Dispersion efficiency is 95 at a filling height of 5 m
%, But it decreases to about 78% at a filling height of 10 m, and it can be seen that the dispersion efficiency further decreases as the filling height becomes longer.

On the other hand, in FIG. 3, the horizontal axis represents the continuous packing height as in FIG. 2 and the vertical axis represents HETP, showing the relationship between the packing height and the rectification efficiency. It shows that HETP gradually increases as the continuous filling height increases, and HETP increases rapidly when the filling height exceeds 10 m.
According to Fig. 3, when the continuous filling height is close to 0, HET
P is about 210 mm. The HETP gradually rises as the filling height increases, but the HETP sharply increases when the filling height is about 12 m. That is, it can be seen that the rectification efficiency per unit filling height decreases when the filling height is about 12 m.

In contrast to the decrease in the rectification efficiency due to the uneven flow generated when the falling liquid passes through the packing, in the rectification column in which the ordered packing shown in FIG. The liquid collecting device 3 and the liquid dispersing device 2 are limited to a certain range.
It is possible to recover the rectification efficiency by setting up and carrying out liquid dispersion again.

FIG. 2 shows that the falling liquid entering the packing material at a dispersion efficiency of 100% (no drift) decreases in dispersion efficiency as the filling height increases, but the dispersion efficiency decreases. To recover the dispersion efficiency (for example, when the filling height is 10 m, the dispersion efficiency ηm = 78% to the maximum ηm =
By recovering to a value close to 100%), the purpose of installing the liquid collecting device and the liquid dispersing device can be achieved. However, when the filling height is 0.5 m or less, the dispersion efficiency ηm does not decrease, and since ηm = 100%, there is a difference that can be recovered even if the liquid collecting device and the liquid dispersing device are installed. Not not. Therefore, the liquid collection device and the liquid dispersion device do not play their roles, and the installation is wasted.

As the lower limit value, in the simulation, the dispersion efficiency is almost 100% at 0.6 to 0.8 m or less and there is no change. However, 0.6 to 0.8 m contains ambiguity, so 0 It is reasonable to set the lower limit to 0.5 m.

The liquid collection device and the liquid dispersion device provided in the rectification column can achieve a dispersion efficiency of at least about 80%. According to FIG. 2, the continuous filling height at which the dispersion efficiency is 80% corresponds to about 10 m. From FIG. 3, when the continuous filling height exceeds 10 m, HETP starts to deteriorate rapidly. Therefore, if the continuous filling height exceeds 10 m, a liquid collecting device and a liquid dispersing device should be installed.

On the other hand, it can be seen from FIG. 2 that the effects of the liquid collecting device and the liquid dispersing device cannot be obtained even if the liquid collecting device and the liquid dispersing device are installed at 0.5 m or less. Therefore, 0.5
It is meaningless to install a liquid collecting device and a liquid dispersing device of m or less.

[0032]

As described above, according to the present invention, in a rectification column in which packings having a regular structure are stacked and packed in a column, the packing height of continuous structured packings is 0.5 m or more and 10 m or more.
To provide an air separation device characterized by using a packed rectification column in which the performance of packing is effectively improved by limiting the range to m or less and installing a liquid collecting device and a liquid dispersing device. Can be done.

[Brief description of drawings]

FIG. 1 is a structural diagram of a rectification column in which a packing having a regular structure is filled in the column.

FIG. 2 is a diagram showing a relationship between continuous packing height and dispersion efficiency of a packing having a regular structure.

FIG. 3 is a diagram showing a relationship between continuous packing height of packing having a regular structure and HETP representing rectification efficiency.

[Explanation of symbols]

1 ... packing having a regular structure, 2 ... liquid dispersion device, 3
... Liquid collector, 4 ... Gas outlet nozzle, 5 ... Liquid inlet nozzle,
6 ... Gas inlet nozzle, 7 ... Liquid outlet nozzle, 8 ... Continuous filling height of packing having a regular structure, A ... Dispersion efficiency when a liquid collecting device and a liquid dispersing device are installed

Claims (5)

[Claims] 1. An air separation apparatus comprising at least one rectification column in which packings having a regular structure are stacked in a column for cryogenic separation of air into nitrogen, oxygen, argon and other gases. In the above, the air is characterized in that the height of the packing is limited to a height at which a predetermined separation efficiency is obtained, and a rectification column provided with a liquid collecting device or a liquid dispersing device between the packings is provided. Separation device. 2. An air separation apparatus comprising at least one rectification column in which packings having a regular structure are stacked in the column for cryogenic separation of air into nitrogen, oxygen, argon and other gases. In the rectification tower, the height of the packing is 0.5 m or more.
An air separation device comprising a rectification column equipped with at least one of a liquid collecting device and a liquid dispersing device for each range of m or less. 3. An air separation apparatus comprising at least one rectification column in which packings having a regular structure are stacked in the column for cryogenic separation of air into nitrogen, oxygen, argon and other gases. In the rectification tower, the height of the packing is 0.5 m or more.
An air separation device comprising a rectification column equipped with a combination of a liquid collection device and a liquid dispersion device at least at one location for each m or less range. 4. Deep cooling of air into nitrogen, oxygen, argon and other gases by using an air separator equipped with at least one rectification column in which packings having a regular structure are stacked in the column. In the air dispersion method of separating, the liquid dispersion method is characterized in that the liquid dispersion is repeated by a liquid collection device or a liquid dispersion device arranged at every predetermined height in the rectification column. 5. An air separation device equipped with at least one rectification column in which packings having a regular structure are stacked in the column is used to deep-cool air into nitrogen, oxygen, argon and other gases. In the air dispersion method for separating, the liquid dispersion is repeated by a liquid collection device or a liquid dispersion device arranged in the rectification column at each height of the packing of 0.5 m or more and 10 m or less. Air dispersion method.