JP6575348B2 - Gas-liquid contact method - Google Patents

Description

  The present invention relates to a gas-liquid contact method. Specifically, it is a gas-liquid contact method in which a gas and a liquid are brought into contact with each other by a shelf tower in which a plurality of shelf boards having weirs and holes are installed, and the height of the weir is predetermined in each stage. Relates to a gas-liquid contact method satisfying

  In the distillation column, mass transfer and heat transfer are performed between the gas and liquid flowing in the distillation column. In order to promote the heat and mass transfer, in other words, in order to increase the distillation efficiency, shelves, packings, etc. are installed in the tower. The role of the shelves and packing is to increase the chance of gas and liquid contact with each other so that the gas and liquid are closer to equilibrium.

  The feature of the packing installed in the distillation column is that the surface area per unit volume (specific surface area) is large. Increasing the chance of gas-liquid contact is achieved by diffusing the supply liquid over a wide surface of the packing. Packing with a large specific surface area gives higher distillation efficiency, but the liquid flow rate per unit surface area decreases, making it difficult to adopt because liquid and gas drifts due to dirt on the surface of the packing and the distillation efficiency tends to decrease. Become.

  A common gas-liquid contact method on the shelf is bubbling. For the liquid held on the shelf plate with a large number of holes, the gas rising from below passes through the holes and vigorously agitates the liquid on the shelf plate, and at the same time, the gas is divided into small bubbles. And increasing the chance of gas-liquid contact. The higher the bubbling, the higher the distillation efficiency, but the pressure of the rising gas is consumed as the driving force, and the differential pressure in the column during operation also increases.

  There are two methods for holding the liquid on the shelf. One is a method in which a weir is provided on the shelf board to maintain a certain range of liquid depth, and a downcomer is installed as a dedicated channel for the liquid that has passed over the weir to descend downward. Since the liquid depth is determined within a certain range by the weir, it can be operated relatively stably even under operating conditions with different liquid and gas flow rates. If there is too little gas to rise, the liquid falls from the hole in the shelf (weeping) and the distillation efficiency is greatly reduced. If too much liquid falls, the downcomer cannot be lowered (downcommer flooding) and the operation of the distillation column becomes impossible. This is the most common specification of a distillation column shelf and is called a “sheet tray”. Other complicated bubble bubbling holes include a bubble cap tray and a valve tray.

  Another method for holding the liquid on the shelf board is to use all of the tower horizontal cross section as a shelf board and provide only a large number of holes on the shelf board. At the same time as the liquid falls from the hole, the gas also rises from the hole. By not having a downcomer, almost all of the tower cross-sectional area can be allocated to the bubbling region, and deposits and the like are less likely to occur due to its simple structure. However, since the liquid depth on the shelf board is based on a delicate balance between the falling liquid and the rising gas, the condition range of the operable liquid and gas flow rate is narrow. In particular, when the liquid depth is shallow, a phenomenon in which the gas rising hole and the liquid falling hole are likely to be separated, and the distillation efficiency is generally low. A dual flow tray with small holes provided at equal intervals on a flat plate is the most common in this embodiment. In addition, a ripple tray provided with small holes on a corrugated plate, a number of slits instead of small holes are provided. There is a turbo grid tray.

In the case of liquids with characteristics such as high viscosity, foaming property, adhesive solid content, etc., the distillation column should be operated stably on the packing that spreads the liquids little by little or on the shelves that bubbling on the shelf. Therefore, a shelf without bubbling is used. It consists of baffles that cover about half of the horizontal section of the distillation tower and is installed in multiple stages in the vertical direction. The baffles adjacent in the vertical direction are arranged at different positions. The gas rises in a zigzag manner to sew between the baffles and comes into gas-liquid contact with the liquid descending from the edge of the baffle. Generally referred to as a baffle tray, it is often not included in the classification table of the distillation column shelf. In Patent Document 1, the distillate from the by-product thermal decomposition apparatus in the acrylic acid production process is distilled and purified by using a disk-type and donut-type baffle to avoid blockage in the distillation column. The method is shown.

  In Patent Document 2, when neutralizing hydrogen fluoride-containing air with an aqueous potassium hydroxide solution, a semicircular shelf board having a weir is used, and a large number of holes are formed in portions overlapping the top and bottom of the shelf so A method for preventing corrosion of the lower surface of the shelf stage by increasing the contact efficiency and making a hole in the support ring is shown.

  In Patent Document 3, when a methacrylic acid-containing gas is absorbed with water using a baffle shelf without a weir, in addition to gas-liquid contact with water descending from the edge of the baffle, a large number of holes are formed on the entire surface of the baffle. It is shown that a gas-liquid contact between the gas passing through the hole and water is possible by providing the gas, and further, blockage by a polymer in the distillation column is avoided.

JP 2003-252824 A Japanese Utility Model Publication No. 56-35202 JP 2001-46802 A

  A plate tower (eg, a collection tower) that has a baffle shelf that is effective for stable operation with a simple structure has been further improved in terms of efficiency, but the flow rate of liquid and gas in the plate tower However, it is still insufficient in terms of stability against fluctuations in liquid properties, etc., and changes with time due to contamination.

  In the case of Patent Document 1 using a disk and a donut-type baffle, even if dirt adheres to the baffle, it does not hinder the flow of liquid or gas and does not hinder continued operation. However, since the liquid flowing on the baffle flows so as to avoid the deposits, the liquid flow that was originally distributed uniformly is biased. As the liquid falls, the resistance increases, and the gas rises so as to avoid this, so that the distillation efficiency is greatly reduced.

  In Patent Document 2, since the columnar liquid continuously falls from the hole opened in the baffle, and the gas flows so as to cross this, the gas-liquid contact at the part is maintained, but the liquid falls from the hole. The ratio of the liquid that drops and the liquid that drops over the weir varies depending on the operating conditions and is not constant. In particular, when the liquid is foamed, the pressure difference between the upper and lower sides of the shelf rises due to the narrowing of the gas flow path, and the increase in the differential pressure dulls the liquid drop from the hole and drops over the weir. This causes a vicious cycle of further narrowing the gas flow path and further increasing the differential pressure.

  When a large number of holes are provided on the entire surface of a baffle that does not have a weir as in Patent Document 3, bubbling in the hole can occur only under very limited operating conditions, but on a baffle that does not have a weir. Since the liquid depth is shallow and the resistance when the gas passes through the hole is small, it is separated into a hole where only the gas rises and a hole where only the liquid falls, and the distillation efficiency is extremely lowered. The shelves installed in the tower in an inclined manner and their support rings have an elliptical shape, and the load in manufacturing and installing the equipment is high, so the adoption is limited.

  An object of the present invention is to solve the above-mentioned conventional problems and to provide a gas-liquid contact method capable of stably making a gas-liquid contact even when operating conditions fluctuate.

  As a result of repeated studies to solve the above problems, the present inventor used a baffle tray having a large number of holes for dropping the liquid on the shelf and a weir for holding the liquid on the shelf. In the operation of a tray tower, it is noticed that the ratio of the liquid falling from the hole on the shelf and the liquid falling over the weir changes, causing a variation in the differential pressure in the shelf. It has been found that by adopting a specification that drops from a hole on the shelf without exceeding the weir, stable gas-liquid contact can be maintained without causing a differential pressure fluctuation in the shelf tower due to operational fluctuations.

The present invention has been achieved based on such findings, and the gist thereof is as follows.
[1] A gas-liquid contact method in which a gas and a liquid are brought into contact with a shelf tower in which a plurality of shelf boards having weirs and holes are installed,
A gas-liquid contact method in which the height (h) of the weir satisfies the following formula (1) in each stage.

(Where h is the height of the weir (m), V is the flow rate of liquid in the tower (m ³ / s), S is the total area of the aperture (m ² ), and g is the acceleration of gravity (m / s ² ) Represents.)
[2] In a method for producing acrylic acid, which includes an acrylic acid production step of oxidizing propylene to obtain crude acrylic acid containing acrylic acid,
A method for producing acrylic acid, wherein the production step comprises the gas-liquid contact method according to [1].

  ADVANTAGE OF THE INVENTION According to this invention, the method of performing the stable gas-liquid contact irrespective of a driving | running | working fluctuation | variation can be provided.

It is a schematic diagram in the collection tower which concerns on one embodiment of this invention. It is a schematic diagram in the collection tower which concerns on one embodiment of this invention. It is a schematic diagram of the acrylic acid collection tower which concerns on one embodiment of this invention. It is explanatory drawing which showed the liquid and gas flow in a collection tower. (A) Sheep tray, (B) Dual flow tray, (C) Baffle tray, (D) Baffle tray with weirs and holes, (E) Baffle tray with holes on the entire surface of the shelf board, (F) of the present invention It is a baffle tray concerning one embodiment.

  Hereinafter, the gas-liquid contact method of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and various modifications are made within the scope of the gist of the present invention. can do.

The present invention relates to a gas-liquid contact method in which a gas and a liquid are brought into contact with each other by means of a shelf tower in which shelves having a weir and a hole are installed in multiple stages. In each stage, the height (h) of the weir Is a gas-liquid contact method satisfying the following formula (1).

(Where h is the height of the weir (m), V is the flow rate of liquid in the tower (m ³ / s), S is the total area of the aperture (m ² ), and g is the acceleration of gravity (m / s ² ) Represents.)

  In the gas-liquid contact method of the present invention, the number of plates in the plate column is usually multistage, and is usually 3 or more, preferably 4 or more, more preferably from the viewpoint of obtaining the number of theoretical plates necessary for distillation separation. Is 5 or more. On the other hand, from the viewpoint of preventing the tower height of the plate tower from becoming excessively high, it is usually 40 or less, preferably 30 or less, and more preferably 25 or less. Moreover, the specific aspect of a plate tower is not specifically limited, For example, an absorption tower, a stripping tower, a collection tower, a distillation tower etc. are mentioned so that it may mention later.

  The application destination of the gas-liquid contact method of the present invention is not particularly limited, and the application destination is wide, for example, when a gas containing a harmful chemical substance such as desulfurization from exhaust gas, carbon dioxide removal, deacidification gas is absorbed in the liquid. . For example, in the case of using a plate tower as an absorption tower, gas containing harmful chemical substances is absorbed into the liquid, and by satisfying the configuration and conditions of the present invention, gas-liquid contact is efficiently performed without increasing the differential pressure. Implemented and operated stably for a long time. In the case where a plate tower is used as the stripping tower, a useful chemical substance in the gas is absorbed in the liquid as much as possible, and then the residual gas is stripped into the atmosphere. Also by satisfying the configuration and conditions of the present invention, the gas-liquid contact is efficiently performed and the operation is stably performed for a long time without increasing the differential pressure.

  Moreover, the gas-liquid contact method of this invention is applicable to manufacture of acrylic acid, manufacture of polyalkylene ether glycol diester, manufacture of polytetramethylene ether glycol diacetate, etc., for example. In the following, the application destination is described as a production method of acrylic acid, more specifically, as a production step of crude acrylic acid in the production method of acrylic acid, but the application destination of the gas-liquid contact method of the present invention is limited to this. I don't mean.

Acrylic acid is usually obtained by a production method including an acrylic acid production step in which propylene is oxidized to obtain crude acrylic acid containing acrylic acid. Further, a purification step for purifying the crude acrylic acid may be included. Specifically, propylene is made into a crude acrylic acid-containing gas by a gas phase catalytic oxidation reaction with an oxygen-containing gas, the crude acrylic acid-containing gas is made into an acrylic acid solution with a solvent such as water in a collection tower, and then distilled. The solvent used for collection is separated into crude acrylic acid, and further purified acrylic acid is obtained by separating impurities by distillation and / or crystallization.
The gas-liquid contact method of the present invention is preferably applied to a collection tower which is a plate tower in the production step of obtaining an acrylic acid-containing liquid in the acrylic acid production method.

FIG. 1 is a schematic view in a collection tower in one embodiment of the gas-liquid contact method of the present invention.
1 is a tower wall of the collection tower, 2 is a shelf board, and the installation position and / or shape is different for each stage so that the section of the collection tower is completely covered by the adjacent upper and lower shelf boards. Placed in. The total cross-sectional area of the two upper and lower shelf plates must be at least 1 times the cross-sectional area of the collection tower in order to completely cover the cross-section of the collection tower. In order not to slip through the shelf board, 1.05 times or more is required substantially, and 1.1 times or more is more preferable. The larger the ratio, the narrower the gas flow passage, that is, the portion not covered by the shelf board, so that it is preferably less than 1.5 times, more preferably less than 1.3 times. The areas of the two upper and lower shelves need not be equal, but the ratio is preferably in the range of 0.9 to 1.1 from the viewpoint of securing a gas flow path.

  3 is a hole provided on the shelf board, and is mainly provided at the place where the upper and lower shelf boards overlap. A hole can be provided in addition to the location, but in this case, the liquid that has fallen from the hole passes through the side of the shelf below it and reaches the shelf below the second level, and the gas-liquid contact This is disadvantageous. Therefore, it is preferable that the number of holes provided in the non-overlapping portions is half or less than the number of holes provided in the overlapping portions.

  In order to eliminate the unevenness of the falling liquid, it is preferable that the hole diameter is the same and the object is arranged with high objectivity. If the hole diameter is small with respect to the plate thickness, the friction when the liquid passes increases, which causes the liquid to be prevented from falling. Therefore, the hole diameter is preferably at least 3 times, more preferably 4 times or more the plate thickness. It is. Further, in order to reduce the influence of the surface tension of the liquid, the hole diameter is preferably at least 5 mm or more, more preferably 8 mm or more. If the hole diameter is too large, the number of holes will decrease, making it difficult to arrange the holes uniformly, and the surface area formed by the liquid column falling from the holes will also decrease, reducing the efficiency of gas-liquid contact. 20 mm or less is preferable, More preferably, it is 15 mm or less.

  When the interval between the holes is narrow, the liquid columns formed by the liquid falling from the holes are likely to merge with each other. Therefore, the center-to-center distance between adjacent holes is preferably at least twice the hole diameter. Although there is no restriction on the upper limit of the center-to-center distance, the longer the distance is, the more difficult it is to arrange the necessary number of holes on the shelf board.

Reference numeral 4 denotes a weir provided around the shelf and not in contact with the inner wall surface of the tower. When the liquid existing at the liquid depth h _L (m) on the shelf plate falls from the hole provided on the plate, if the friction or the like is ignored, the drop velocity v (m / s) from the liquid hole = It is expressed as (2gh _L ) ^1/2 . If the liquid flow rate in the tower during the operation of the collection tower is V (m ³ / s), the total area of the openings on the shelf is S (m ² ), and the acceleration of gravity is g (m / s ² ), h _L = (V / S) ² / 2g, but in actuality, friction or the like occurs, so h _L becomes larger. Once there is a state where the liquid flows over the weir, it may not easily return to the original state, so a sufficient weir height is required, at least 3.2 times the calculated value above, More preferably, 3.5 times or more is required. That is, the weir height h (m) provided on the shelf board needs to satisfy 8 × (V / S) ² / 5g. However, regardless of each numerical value, h is preferably 20 mm or more for the purpose of maintaining a stable liquid depth. In addition, the higher the h, the lower the possibility that the liquid will flow over the weir, but it will narrow the gas flow path, so it should be avoided to make it too high, preferably less than 200 mm, more preferably It is less than 150 mm.

  FIG. 2 is a schematic view inside the collection tower in one embodiment of the gas-liquid contact method of the present invention. By increasing the target property of the shelf board, the flow of liquid and gas is made more uniform, and stable gas-liquid contact can be performed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

[Comparative example]
Using the apparatus shown in FIG. 3, acrylic acid was collected from an acrylic acid-containing gas obtained by a catalytic gas phase oxidation reaction of propylene. 21 is a collection tower main body, 22 is a supply line for acrylic acid-containing gas, 23 is a seven-stage baffle tray provided at the bottom of the tower, 24 is a tower bottom circulation line equipped with a cooling device in the middle, and 25 is collected. An acrylic acid aqueous solution extraction line, 26 is a dual flow tray, 27 is a bubble cap tray, 28 is an exhaust gas line at the top of the column, and 29 is a supply line for water for collection.

The gas flow rate in the baffle tray section is 16 to 20 t / h, the superficial velocity in the tower is 1.2 to 1.8 m / s, the liquid flow rate in the tower is 160 to 165 m ³ / h, and the shape of the baffle tray is 7 All the stages are the same, and the ratio to the cross-sectional area of the tower is about 3/4, the hole diameter on the baffle tray is 12 mm, the distance between adjacent holes is 30 mm, and the liquid falling rate from the aperture is 0. It was 60 to 0.62 m / s. During the continuous operation for one year, the differential pressure in the baffle tray increased several times, and the differential pressure increase was alleviated by introducing an antifoaming agent and reducing the operating load each time. Weir height of the baffle tray is 39 mm, was 2 to 2.2 times the value calculated from ^{(V / S) 2 / 2g} .

[Example]
The operation was performed in the same manner as in the comparative example except that the height of the baffle tray was changed to 72 mm. During the operation period of 3 years, no increase in differential pressure in the baffle tray was confirmed. Weir height was 3.7 to 3.9 times the value calculated from ^{(V / S) 2 / 2g} . In addition, in the confirmation in the tower when the operation is stopped, there is a significant difference in dirt between the upper side and the lower side of the weir facing the shelf side, and the liquid in the tower does not flow over the weir during the operation period. It was confirmed that

DESCRIPTION OF SYMBOLS 1,11 Tower wall of collection tower 2,12 Shelf 3,13 Hole provided on shelf 4,14 Weir 21 Collection tower main body 22 Supply line of acrylic acid containing gas 23 Baffle tray 24 Tower bottom circulation line 25 Acrylic acid aqueous solution extraction line 26 Dual flow tray 27 Bubble cap tray 28 Exhaust gas line at the top of column 29 Water supply line for collection

Claims (2)

A gas-liquid contact method in which a gas and a liquid are brought into contact with a shelf tower in which a multi-stage shelf board having a weir and a hole is installed,
In each stage, the height of the weir (h) is smaller than the formula (1),
A gas-liquid contact method, wherein the hole has a diameter of 20 mm or less .

(Where h is the height of the weir (m), V is the flow rate of liquid in the tower (m ³ / s), S is the total area of the aperture (m ² ), and g is the acceleration of gravity (m / s ² ) Represents.)
In the method for producing acrylic acid, which includes an acrylic acid production step of oxidizing propylene and obtaining crude acrylic acid containing acrylic acid,
A method for producing acrylic acid, wherein the production step comprises the gas-liquid contact method according to claim 1.

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