JPS621402A - Gas-liquid contact device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a gas-liquid contact device, and more particularly, to a gas-liquid contact device using a perforated plate having a downcomer.

[Background of the invention]

Gas-liquid contact equipment equipped with a perforated plate with a downcomer has low pressure loss, high rectification performance, and simple structure, so it is suitable for various gas-liquid contact applications in the chemical industry such as distillation, rectification, and absorption. Widely used in operations.

FIG. 1 shows a perforated plate of a gas-liquid contacting device according to the invention. A feature is that a communication pipe 2 is installed on the lower surface of a conventional perforated plate 1 to form a flow path for liquid air.

The principle of a gas-liquid contact device will be explained using FIG. 2, taking a gas-liquid contact device for separating air as an example.

The gas-liquid contact device has a double rectification column structure in which an upper column 15 and a lower column 16 are connected by a main condenser 17. Upper tower, lower tower Ki
, several ten stages fi1 of perforated plates 1 (shown in FIG. 3), which are obtained by removing the communicating tubes from the perforated plates shown in FIG. 1, are provided.

A perforated plate 1rcfl, a downcomer 3 are installed, and the third
As shown in the figure, the liquid 18 (liquid air) flows on the perforated plate 1, passes through the downcomer 3, flows down to the perforated plate below, and the gas 1
9 (raw air) rises through the holes of the perforated plate 1.

Perforated plates can be classified according to the liquid flow method, including swirling flow type, cross flow type, unidirectional flow type, etc. For perforated plates with swirling flow type, there are 1-way flow plate, 2-way flow plate, etc. depending on the number of branched flows. They are classified as 4-way flow plates and 6-way flow plates (as shown in Figure 4).

In the gas-liquid contact device shown in FIG. 2, liquefied raw air is separated by rectification into oxygen 20 and nitrogen 21.

Nitrogen has a lower boiling point than oxygen, so it evaporates easily (the boiling point at 1 atmosphere is nitrogen - 1960, oxygen -
183C). To keep this in mind, steam contains a lot of nitrogen and liquid contains a lot of oxygen.

By further liquefying this vapor and repeating evaporation, the concentrations of nitrogen in the vapor and oxygen in the liquid increase. Evaporation occurs on perforated plates installed in the upper and lower columns.

In the lower tower section of the gas-liquid contactor, a liquid containing a large amount of nitrogen, liquefied by the main condenser, flows over the perforated plate 1, as shown in FIG. 3, and falls through the downcomer 3. The raw air gas enters the rectification column from the lower part of the lower column section, enters the liquid through the holes 4 of the perforated plate 1, foams, forms a VC foam layer 6 at the top of the liquid 5, and rises roughly. do. In the upper column, the nitrogen-rich liquid produced in the lower column is injected from the center, and the oxygen-rich liquid is injected from the center, and the perforated plate is lowered. When the efficiency (stage efficiency) of one stage is constant, the greater the number of stages, the higher the efficiency of distillation, rectification, etc.

Therefore, considering the case where the tower height is constant, efficiency is higher if the stage interval (H in FIG. 1) is decreased or the number of stages is increased. However, if the stage interval is made too small, pressure loss abnormalities may occur due to partial foaming due to the following process.

(1) Partial foaming occurs on the lower perforated plate of perforated plate 1 shown in Fig. 3 due to uneven liquid depth distribution and uneven flow of rising gas, and the foam layer generated by the foaming is transferred to the upper perforated plate. contact the bottom surface of the

(2) Due to the foam layer contacting the upper layer on the perforated plate, the 5th
As shown in the figure, a gas flow path 10 is formed.

(3) Through this gas flow path, the gas remains in the same position and promotes foaming on the upstream side of the upper perforated plate, that is, the area where the liquid depth is large.

(4) Also in the upper perforated plate, the foam layer contacts the upper perforated plate to form the gas flow path 10.

(5) This phenomenon reaches the upper porous plate and increases.

When such a phenomenon occurs, the drying pressure loss due to viscous resistance when gas passes through the holes 4 of the porous plate is given by: Here, ε. The key constant, ρg, is the density of the gas. Therefore, when the foam layer comes into contact with the upper stage, the gas flow path 10 is formed as described above, and when the gas flow rate increases, ΔPd increases, and pressure abnormality with large pressure loss may occur. When such an abnormal pressure loss occurs, it becomes difficult to blow gas at the rated flow rate into the gas-liquid contact device, and the efficiency of distillation and rectification by gas-liquid contact is significantly reduced.

Therefore, since the liquid depth difference on the perforated plate and the uneven flow of the rising gas cause partial foaming, Japanese Patent Laid-Open No. 56-33
In the conventional gas-liquid contact device described in No. 005, the perforated plate provided in the tower is dammed so as to be gradually higher in the radial direction from the center of the tower. By making the liquid depth on the inner circumferential side almost the same as the inner circumferential side, and as a result, the rising gas is made uniform, pressure loss is reduced without deteriorating performance. Further, means for gradually decreasing the pore diameter of the perforated plate from the center of the tower in the radial direction;
Alternatively, a method is used in which the pitch of the holes is gradually increased from the center of the tower in the radial direction, thereby making the static liquid depth uniform.

However, the inclination angle of the perforated plate depends on the liquid flow rate and the rising gas flow rate, so even if the optimum inclination angle can be set at the time of rating, if the liquid and gas flow rates differ from the rated values, the inclination angle on the perforated plate will change. The liquid depth is not necessarily uniform. Maku,
Making the perforated plate, which requires the most manufacturing cost in a gas-liquid contact device, into a conical shape with an inclination, and changing the hole diameter or hole arrangement pitch in the radial direction reduces the manufacturing cost of the entire gas-liquid contact device. It will also increase it significantly.

[Purpose of the invention]

The purpose of the present invention is to prevent partial foaming caused by uneven flow of rising gas by preventing contact between the foam layer on the perforated plate and the upper perforated plate, and to suppress the propagation of abnormal pressure loss phenomena. It is in.

[Summary of the invention]

In order to achieve this purpose, the gas-liquid contact device of the present invention avoids the need to improve the perforated plate, which is expensive to manufacture, and installs a communication pipe at the bottom of the conventional perforated plate, so that the foam layer on the perforated plate can When the temperature exceeds this value, the liquid is allowed to flow out through the communication pipe to lower the depth of the liquid in the foaming section. As a result, even when the stage interval is small, it is possible to prevent the occurrence and propagation of abnormal pressure loss, and to manufacture a highly efficient gas-liquid contact device.

That is, one end of the communication pipe is installed on the lower surface of the perforated plate,
The above objective is achieved by placing the opening at the other end at a position higher than the perforated plate by ΔL. The height of this communication pipe can be determined as follows.

It is known that the relative foam density φf, which is the ratio of the maximum static liquid depth ht to the foaming height hrO, and the rising gas velocity Yg have the relationship shown in FIG. In order to cause the liquid to flow out, K must also be smaller than the maximum static liquid depth hL in the event of an abnormality.

In other words, ΔL<ht...(2) Please note that the foam layer height hf must be smaller than the step interval H, which is a condition for the foam layer not to come into contact with the upper step, so ht≦H...(3) Become.

Therefore, ΔL is defined by the relative foam density formula φr=-!
Using La− (4) and the above relationship, it is expressed as hf ΔL≦Hφf (5).

ΔLi needs to be higher than the maximum liquid depth hrl during normal operation near the perforated plate penetrated by the communication pipe, so hn
<ΔL, (6).

Therefore, if ΔL is determined so as to satisfy hn<ΔL≦Hφ, (7), a communication pipe that can achieve the above objective can be obtained.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a schematic diagram showing an embodiment of a gas-liquid contact device according to the present invention. This figure shows a cross-sectional view of a perforated plate of a unidirectional flow type gas-liquid contact device. A communication pipe is installed at the bottom of the perforated plate.
The other end of the communicating tube with holes is installed in the space between the perforated plate and the upper perforated plate, and its height ΔL is
The relationship in equation (7) is satisfied. Under normal operating conditions,
Since ΔL is also larger than the maximum static liquid depth hn during normal operation, the liquid does not flow out through the communication pipe, and the contact area between the liquid and the gas does not decrease and the stage efficiency does not decrease. On the other hand, partial foaming occurs in the lower perforated plate, and the foam layer reaches the upper perforated plate.
When the gas flow path is formed, the foam layer begins to rise even in the upper perforated plate due to the increase in gas flow rate. However, before the foam layer reaches the upper perforated plate, the depth of the liquid in the foam section exceeds the height ΔL of the communicating tube, and as shown in Figure 7, the liquid flows from the other end of the communicating tube. leak. In addition to this, the foam layer
This prevents the gas from reaching the upper perforated plate and forming the gas flow path 10, preventing abnormal pressure loss from occurring and maintaining a predetermined gas-liquid contact efficiency.

An embodiment of the present invention using a two-way flow plate of a swirling flow type as shown in FIG. 4 is shown in FIGS. 8 and 9.

FIG. 8 is a perspective view of a part of the two-way flow plate where there is a downcomer from the upper stage to the lower stage, and FIG. 9 is a perspective view of the part 180 degrees opposite to that of FIG. Such detailed flow conditions on the perforated plate can be numerically determined by a flow analysis program that deals with the flow of liquid and bubbles, the pores on the perforated plate, and the free surface. The results obtained by numerical analysis are
It is shown in FIG. 0, FIG. 11, and FIG. 12. The liquid that has fallen through the downcomer flows into the perforated plate, and due to centrifugal force, the liquid depth increases from the inner circumference to the outer circumference of the perforated plate, as shown in Fig. 1θ. However, a pressure gradient occurs due to the difference in liquid depth, and the flow tries to return toward the center.
In the end, the liquid flows along the circumferential direction as shown in FIG. Figure 812 shows the change in liquid depth in the same direction on a perforated plate using a two-way flow system. In the figure, the dashed line indicates the static liquid depth distribution at the outer circumference, the broken line at the inner circumference, and the solid line at the radial center. As can be seen from this figure, on the perforated plate, the maximum liquid depth occurs at the outer periphery of the inlet, and the minimum liquid depth occurs at the inner periphery of the outlet. In the example shown in Figures 8 and 9, one end of the communicating pipe is installed on the perforated plate at the outer periphery of the inlet where the liquid flowing down through the downcomer begins to flow on the perforated plate, that is, at the location where the maximum liquid depth occurs. (see FIG. 8), a communication pipe is passed through the innermost periphery of the lower surface of the perforated plate, and the other end of the communication pipe is installed at the outer periphery of the outlet, that is, at the location where the minimum liquid depth is generated.

In this example, since the communication pipe is installed on the bottom surface of the part of the perforated plate where the maximum static liquid depth is, the communication pipe can be used to foam more quickly and with more liquid than if it were installed in other parts. It is possible to bypass from

In addition, since the other end of the communication tube is installed at the minimum liquid depth of the perforated plate, the lower limit value of equation (7) becomes smaller and the allowable range of ΔL becomes wider. By setting ΔL as close to the lower limit as possible, it is possible to increase the bypass flow rate through the communication pipe.

If partial foaming occurs, the liquid will flow through the communication pipe, but at this time, pressure loss may occur within the communication pipe, making it difficult for the liquid to flow. Since the pressure loss due to the pipe is proportional to the length of the pipe, as shown in Figure 8, by passing the communicating pipe along the inner periphery of the perforated plate, the pipe length is made to be the shortest distance. Reduces pressure loss.

In addition, in this embodiment, as shown in FIGS. 8 and 9, the communication pipe is arranged at the bottom of the perforated plate on the innermost side where the liquid depth is smallest in the radial direction, so that the communication pipe is This has the effect of creating resistance to the flow of gas, slowing down the gas flow velocity in this part, and making the flow velocity distribution of the rising gas uniform.

A second embodiment of the invention is shown in FIG. In this embodiment, communication pipes are installed in two adjacent stages, upper and lower, in a unidirectional flow gas-liquid contact bag.

As already explained in Fig. 5, after partial foaming occurs on the downstream side of the perforated plate, the foam layer reaches the upper perforated plate, and similar partial foaming occurs on the upstream side of the upper stage. , causing pressure loss abnormality. Partial foaming occurs at the downstream part of the perforated plate, and the foam layer reaches the upper stage.Partial foaming occurs at the upstream part of the upper perforated board, and the foam layer reaches the perforated board above it, and the foam layer reaches the upper stage. Partial foaming will occur. Therefore, if communicating pipes are installed in two stages, upper and lower, as shown in Fig. 13, when foaming occurs downstream of the perforated plate in the lower stage, Vc will be reduced by the liquid flowing into the communicating pipe in the upper stage, resulting in the partial foaming. Lower the liquid depth to prevent the foam layer on the upper perforated plate from reaching the upper layer. When foaming occurs in the upstream part of the lower perforated plate, the VC allows liquid to flow into the lower communicating pipe, lowering the liquid depth in the partially foamed area and preventing the foam layer from reaching the upper stage, resulting in partial foaming. Propagation can be prevented.

Figures 14 and 15 show the second embodiment of the swirling flow system.
This is an example of application to a rectangular plate. Figure 14 shows a two-way flow plate.
15 is a perspective view of a part where there is a downcomer from the upper stage to the lower stage, and FIG. 15 is a perspective view of the part 180 degrees opposite of FIG. 14. One end of the communication pipe for both the upper and lower stages is installed at the outer periphery of the inlet of the perforated plate, and the other end is installed at the inner periphery of the outlet. By installing communication pipes in two consecutive upper and lower stages, it is possible to prevent the foam layer from reaching the upper stage due to partial foaming, and thereby preventing pressure loss abnormalities from propagating throughout the tower of the gas-liquid contact device. In addition, by passing the communication pipe through the innermost periphery and providing an opening at the other end at the inner periphery of the outlet, the effect of reducing the gas flow velocity at the low liquid depth can be achieved, similar to the flcl example. be. In addition, by forming a set of two upper and lower stages and energizing perforated plates with communicating pipes installed every few stages, even when the stage interval is small and the gas flow rate is large, the partially foamed foam layer can reach the upper stage. , it is possible to prevent this phenomenon from propagating to the perforated plate in the upper direction and expanding the pressure loss abnormality.

In the above embodiments, two-way flows such as one-way flow type and swirling flow type were explained, but it goes without saying that similar effects can be obtained in swirling type gas-liquid contact devices such as one-way flow and four-way flow. do not have.

〔Effect of the invention〕

As explained above, according to the present invention, a communication pipe is provided in the lower part of the perforated plate, and the other end with the hole is installed in the space between the perforated plate and the upper stage. When foaming occurs, it is possible to prevent the foam layer of the partially foamed portion from coming into contact with the upper perforated plate, prevent abnormal pressure loss, and realize a gas-liquid contact device with stable operating conditions.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a gas-liquid contact device showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of a large-sized air separation device, FIG. 3 is an explanatory diagram of a conventional gas-liquid contact device, and FIG. The figure shows the swirl flow type 2.
FIG. 5 is an explanatory diagram of a conventional gas-liquid contact device, FIG. 6 is a diagram showing the relationship between gas flow velocity and relative foam density, and FIG. 7 is a diagram of a perforated plate according to the present invention. An explanatory diagram of a gas-liquid contact device showing an embodiment, FIG. 8 is a perspective view of a two-way flow plate type perforated plate showing an embodiment of the present invention, and FIG. 9 shows an embodiment of the present invention. Perspective view of perforated plate of two-way flow plate system, 1st θ
The figure is a two-way flow method on a perforated plate.
Figure 12 is a graph showing the liquid depth distribution on the perforated plate in the two-way flow system, and Figure 13 is a gas-liquid contact diagram showing an embodiment of lX2 according to the present invention. An explanatory diagram of the device, FIG. 14 is a perspective view of a two-way flow plate type perforated plate showing a second embodiment of the present invention, and FIG. 15 is a two-way flow diagram showing a second embodiment of the present invention. A perspective view of a perforated plate using the dish method. DESCRIPTION OF SYMBOLS 1... Perforated plate, 2... Communication pipe, 3... Downcomer, 4... Hole part of perforated plate, 5... Liquid, 6... Foam layer, 7... Liquid receiver Box, 8...Liquid inlet, 9...Perforated plate outer periphery, 10...Gas flow path, 11...Liquid outlet, 12
...Inner periphery of perforated plate.

Claims (1)

[Scope of Claims] 1. A downcomer in which a plurality of perforated plates on the upper surface of which liquid flows are built in in the vertical direction, and the liquid flows down to the lower perforated plate side, and a downcomer that directs the liquid exiting the downcomer to the perforated plate. In the gas-liquid contact device, the gas-liquid contacting device has a liquid receiving box that allows the liquid to flow upward, and contacts the gas rising against the perforated plate with the liquid, in which a communicating pipe is installed on the lower surface of the perforated plate, and an opening in the communicating pipe is provided. A gas-liquid contact device, characterized in that the other end portion thereof is installed in a space between the perforated plate and the upper perforated plate. 2. In claim 1, the height ΔL (mm) of the open end of the communicating pipe installed in the space between the perforated plate on which the communicating pipe is installed and the upper perforated plate satisfies the following conditions: ΔL≦Hφ_f Here, H: Distance between perforated plates installed above and below (mm) φ_
f: Relative foam density (φ_f=h_l/h_f) h_l:
Maximum static liquid depth h_f on the perforated plate: A gas-liquid contact device characterized in that it satisfies the foaming height on the perforated plate.