Manufacturing method of water-absorbent resin

Abstract

This method for producing a water absorbent resin comprises a cleaning step wherein the inside of a heat exchanger is cleaned, said heat exchanger being connected to a container, in which a polymer that is a precursor of the water absorbent resin in the form of a hydrous gel is contained, for the purpose of cooling the gas that is generated within the container and contains the polymer. The heat exchanger is provided with: a plurality of pipes, each of which has a long and thin passage where the gas passes through and is configured such that the gas is cooled by dissipating heat during the time the gas passes through the passage; a chamber which is arranged above the plurality of pipes so as to be in communication with top openings of the plurality of pipes; and a cleaning device that jets a cleaning liquid within the chamber. The cleaning step includes cleaning of at least the inside of the chamber by jetting the cleaning liquid from the cleaning device within the chamber.

Description

[Technical field]

[0001] The present invention relates to a method for producing a water-absorbent resin. [Background technology]

[0002] A water-absorbent resin can be produced by polymerizing a raw material monomer to produce a hydrogel-like polymer, and then drying the polymer. Since heat of polymerization is generated during the polymerization reaction, a heat exchanger is often connected to the polymerization tank in which the polymerization is carried out in order to remove the heat of polymerization. This type of heat exchanger is typically configured to cool and condense the gas sent from the polymerization tank, and then return the gas to the polymerization tank (see Patent Document 1).

[0003] The gas sent to the heat exchanger usually contains polymers. As pointed out in Patent Document 1, these polymers can cause blockages in the heat transfer pipes of the heat exchanger. In order to address this problem, Patent Document 1 proposes that a plate-like member having a plurality of through holes is inclined and attached in a chamber connected to the upstream side of a plurality of heat transfer pipes, and the polymer is collected at a low point on the upper surface of the plate-like member, thereby suppressing blockage of the pipes by the polymers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2013-204860 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even with the method of Patent Document 1, it is still not possible to sufficiently prevent the clogging of the piping, and the piping often becomes clogged. Therefore, it is necessary to periodically stop the operation of the heat exchanger, disassemble it, and clean its inside, which is very troublesome. The same problem may also occur in other heat exchangers connected to a container that contains a hydrous gel-like polymer, such as a concentrator used to distill off liquid components after the polymerization reaction is completed.

[0006] An object of the present invention is to provide a method for producing a water-absorbent resin that can effectively prevent clogging of piping in a heat exchanger. [Means for solving the problem]

[0007] The method for producing a water-absorbent resin according to a first aspect includes a cleaning step of cleaning the inside of a heat exchanger that is connected to a container that contains a hydrogel-like polymer that is a precursor of the water-absorbent resin and that cools a gas containing the polymer generated in the container. The heat exchanger has a long and narrow passage through which the gas passes and includes a number of pipes that are configured to be cooled by dissipating heat while the gas passes through the passages, a chamber that is disposed above the number of pipes and communicates with openings at the upper ends of the number of pipes, and a cleaner that sprays a cleaning liquid in the chamber. The cleaning step includes cleaning at least the inside of the chamber by spraying the cleaning liquid from the cleaner in the chamber.

[0008] A method for producing a water-absorbent resin according to a second aspect is the method according to the first aspect, wherein the cleaning machine is configured to spray the cleaning liquid toward at least an inner wall surface of the chamber.

[0009] A manufacturing method for a water-absorbent resin according to a third aspect is the manufacturing method according to the second aspect, wherein the cleaning machine is configured to spray the cleaning liquid toward at least a top surface included in the inner wall surface of the chamber.

[0010] A method for producing a water-absorbent resin according to a fourth aspect is the method according to any one of the first aspect to the third aspect, wherein the cleaning machine rotates around a first axis extending in a first direction while rotating around a second axis extending in a second direction intersecting the first direction, and has an injection port configured to inject the cleaning liquid while rotating around the first axis and the second axis.

[0011] A method for producing a water-absorbent resin according to a fifth aspect is the method according to any one of the first aspect to the fourth aspect, wherein the container is a polymerization tank for polymerizing monomers that are raw materials for the water-absorbent resin.

[0012] A method for producing a water-absorbent resin according to a sixth aspect is the method according to any one of the first aspect to the fifth aspect, wherein the cleaning step includes removing the polymer lumps adhering to at least one of an inner wall surface of the chamber and an inner wall surface of the pipe by spraying the cleaning liquid from the cleaning machine in the chamber.

[0013] A method for producing a water-absorbent resin according to a seventh aspect is the method for producing a water-absorbent resin according to the sixth aspect, wherein the washing step includes spraying the washing liquid toward an inner wall surface of the chamber, thereby crushing and dropping off lumps of the polymer adhering to the inner wall surface. Effect of the Invention

[0014] According to the above-mentioned aspect, a cleaning liquid is sprayed through a cleaning machine into a chamber that is disposed above a number of pipes in a heat exchanger and communicates with the openings at the upper ends of the number of pipes. This makes it possible to remove the hydrogel-like polymer, which is a precursor of the water-absorbent resin adhering to the inside of the chamber, and as a result, it is possible to effectively prevent clogging of the pipes. In addition, as a result, it is possible to efficiently produce the water-absorbent resin. [Brief description of the drawings]

[0015] [Figure 1] 1 is an overall configuration diagram of a water-absorbent resin manufacturing apparatus according to an embodiment; [Diagram 2]FIG. 2 is a cross-sectional side view of a heat exchanger according to an embodiment. [Diagram 3] Graph showing the cleaning effect according to Example 1. [Figure 4] Graph showing the cleaning effect according to Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a method for producing a water-absorbent resin according to one embodiment of the present invention will be described with reference to the drawings.

[0017] <1. Water-absorbent resin manufacturing equipment> 1 shows an overall configuration diagram of a water-absorbent resin manufacturing apparatus 100 used to carry out the manufacturing method of the water-absorbent resin according to the present embodiment. Water-absorbent resins are widely used in various applications, such as sanitary materials such as paper diapers and sanitary products, daily necessities such as pet sheets, industrial materials such as water-absorbent sheets for food, water-stopping materials for cables, and condensation prevention materials, water-retaining agents and soil conditioners for greening, agriculture, and horticulture. Water-absorbent resins are manufactured by polymerizing monomers as raw materials to produce polymers.

[0018] As shown in FIG. 1, the water-absorbent resin manufacturing apparatus 100 includes a polymerization vessel 1 and a concentrator 2. The polymerization vessel 1 prepares a slurry containing a hydrogel-like polymer (a liquid containing a hydrogel-like polymer) by polymerizing a monomer serving as a raw material of the water-absorbent resin. The concentrator 2 concentrates the slurry by distilling off liquid components from the slurry sent from the polymerization vessel 1, thereby preparing a concentrated liquid of the polymer. The manufacturing apparatus 100 further includes a dryer 3, which dries the concentrated liquid of the polymer sent from the concentrator 2 (i.e., volatilizes the liquid components). When a hydrogel-like polymer is produced by the reversed-phase suspension polymerization method, the liquid components mainly contain a hydrocarbon dispersion medium and water, and when a hydrogel-like polymer is produced by the aqueous solution polymerization method, the liquid components mainly contain water.

[0019] 1, the production apparatus 100 includes two heat exchangers 4A and 4B. During the polymerization reaction in the polymerization vessel 1, polymerization heat is generated, and during the concentration treatment in the concentrator 2, the slurry is heated. The heat exchanger 4A is connected to the polymerization vessel 1 and removes the polymerization heat. The heat exchanger 4B is connected to the concentrator 2 and removes the heat applied during the concentration treatment.

[0020] 1, the production apparatus 100 further includes a control device 5 that controls the operations of the polymerization vessel 1, the concentrator 2, the dryer 3, and the heat exchangers 4A and 4B, thereby controlling the production process of the water absorbent resin. The control device 5 is typically realized as a computer controlled by a program.

[0021] The polymerization vessel 1, the concentrator 2, the dryer 3, and the heat exchangers 4A and 4B will be described in detail below, with reference to various devices connected to these devices 1, 2, 3, 4A, and 4B as appropriate.

[0022] <2. Configuration of each part> <2-1. Polymerization vessel> The polymerization vessel 1 has a polymerization tank 10. The polymerization tank 10 is a container in which a monomer, for example, a water-soluble ethylenically unsaturated monomer, which is a raw material for the water-absorbent resin, and a liquid component are contained so that a gas phase component is formed at the top. In the polymerization tank 10, the monomer and the liquid component are appropriately stirred by a stirrer (not shown) and heated by a heating device (not shown), whereby a polymerization reaction of the monomer progresses and a hydrogel-like polymer is produced. These stirrers and heating devices are connected to a control device 5, and their operations are controlled. As a result, a slurry containing a hydrogel-like polymer, which is a precursor of the water-absorbent resin, is contained in the polymerization tank 10.

[0023] The polymerization tank 10 has openings 11 and 12 at the top. One end of a pipe L1 is connected to the opening 11 at the top, and the other end of the pipe L1 is connected to an opening 41 of a heat exchanger 4A described below. Gas heated by heat of polymerization accompanying the polymerization reaction is discharged from the opening 11, passes through the pipe L1, and flows into the heat exchanger 4A via the opening 41. A valve V1 is attached to the pipe L1, and the opening and closing of the valve V1 is controlled by the control device 5 to control the communication of gas through the pipe L1.

[0024] One end of another pipe L2 is connected to the other upper opening 12, and the other end of the pipe L2 is connected to an opening 42 of a heat exchanger 4A described below. The gas sent from the polymerization tank 10 to the heat exchanger 4A is cooled and condensed in the heat exchanger 4A to become a cooling fluid containing liquid and gas. This cooling fluid is discharged from the opening 42, passes through the pipe L2, and flows into the polymerization tank 10 via the opening 12. In this way, the polymerization heat in the polymerization tank 10 is removed. A valve V2 is attached to the pipe L2, and the opening and closing of the valve V2 is controlled by the control device 5 to control the communication of the cooling fluid through the pipe L2.

[0025] The polymerization tank 10 has an opening 13 at the bottom. One end of a pipe L3 is connected to the opening 13 at the bottom, and the other end of the pipe L3 is connected to an opening 21 of the concentrator 2 described below. Slurry produced by a polymerization reaction in the polymerization tank 10 is discharged from the opening 13, passes through the pipe L3, and flows into the concentrator 2 via the opening 21. A valve V3 is attached to the pipe L3, and the opening and closing of the valve V3 is controlled by the control device 5 to control the communication of the slurry through the pipe L3.

[0026] <2-2.Concentrator> The concentrator 2 has a concentration tank 20, which has openings 21, 22, and 23 at the top. The opening 21 at the top is connected to the opening 13 of the polymerization tank 10 via the pipe L3 as described above. The concentration tank 20 is a container in which the slurry sent from the polymerization tank 10 via the pipe L3 is stored so that a gas phase component is formed at the top. In the concentration tank 20, the slurry is appropriately stirred by a stirrer (not shown) and heated by a heating device (not shown), whereby the liquid components contained therein are distilled off and the slurry is concentrated. These stirrers and heating devices are connected to the control device 5, and their operations are controlled. As described above, the concentration tank 20 contains a concentrated liquid containing a hydrogel-like polymer that is a precursor of a water-absorbent resin.

[0027] One end of another pipe L4 is connected to another opening 22 at the top, and the other end of the pipe L4 is connected to an opening 41 of a heat exchanger 4B described later. Gas heated during the concentration process is discharged from the opening 22, passes through the pipe L4, and flows into the heat exchanger 4B via the opening 41. A valve V4 is attached to the pipe L4, and the opening and closing of the valve V4 is controlled by the control device 5 to control the communication of gas through the pipe L4.

[0028] One end of yet another pipe L5 is connected to yet another opening 23 at the top, and the other end of the pipe L5 is connected to an opening 42 of a heat exchanger 4B described later. The gas sent from the concentration tank 20 to the heat exchanger 4B is cooled and condensed in the heat exchanger 4B to become a cooling fluid containing liquid and gas. This cooling fluid is discharged from the opening 42 and passes through the pipe L5, and its oily components flow into the concentration tank 20. In this way, heat is removed from the concentration tank 20. A valve V5 is attached to the pipe L5, and the opening and closing of the valve V5 is controlled by the control device 5 to control the communication of the cooling fluid through the pipe L5.

[0029] In this embodiment, the pipe L5 is equipped with an oil separator D1. The oil separator D1 is used when preparing a polymer by the reversed-phase suspension polymerization method, and may not be used when the aqueous solution polymerization method is adopted. The oil separator D1 is a device that separates an oil component (hydrocarbon dispersion medium) and an aqueous component from a liquid component, and is connected to a recovery vessel D2 via a pipe L7 branched from the pipe L5. The aqueous component separated from the cooling fluid in the oil separator D1 is discharged outside the system without being returned to the concentration tank 20, and is recovered in the recovery vessel D2. This allows the dehydration of the slurry in the concentration tank 20 to be promoted. Meanwhile, the oil component separated from the cooling fluid in the oil separator D1 is returned to the concentration tank 20 via the opening 23.

[0030] Alternatively, the opening 23, the valve V5, the oil separator D1, etc. may be removed, and the cooling fluid discharged from the opening 42 of the heat exchanger 4B may be entirely discharged outside the system and recovered in the recovery vessel D2. In this case, it is preferable to add an oily component to the concentration tank 20 as appropriate.

[0031] The concentration tank 20 has an opening 24 at its lower part. One end of a pipe L6 is connected to the lower opening 24, and the other end of the pipe L6 is connected to an opening 31 of the dryer 3, which will be described later. A concentrated liquid produced by the concentration process in the concentration tank 20 is discharged from the opening 24, passes through the pipe L6, and flows into the dryer 3 via the opening 31. A valve V6 is attached to the pipe L6, and the opening and closing of the valve V6 is controlled by the control device 5 to control the communication of the concentrated liquid through the pipe L6.

[0032] <2-3. Dryer> The dryer 3 has a drying chamber 30, which has an opening 31 at its upper part. The upper opening 31 is connected to the opening 24 of the concentration tank 20 via the pipe L6 as described above. The drying chamber 30 receives the concentrated liquid sent from the concentration tank 20 via the pipe L6, and dries the polymer of the water-absorbent resin contained in the concentrated liquid by heating the concentrated liquid with a heating device (not shown). This heating device is connected to the control device 5, and its operation is controlled.

[0033] The concentrator 2 and the heat exchanger 4B connected thereto may be omitted, and the polymerization vessel 1 may be directly connected to the dryer 3. In this case, the dryer 3 will simultaneously concentrate and dry the slurry.

[0034] <2-4.Heat exchanger> Next, the structures of the heat exchangers 4A and 4B will be described with reference to Fig. 2. Since the heat exchangers 4A and 4B have the same structure, they will not be distinguished from each other and will be referred to as the heat exchanger 4, and their structures will be described collectively.

[0035] The heat exchanger 4 is a device for cooling gas containing a hydrogel-like polymer, which is a precursor of a water-absorbent resin, generated in the polymerization tank 10 or the concentration tank 20. The heat exchanger 4 has a casing 40. The casing 40 has a cylindrical body 401, a dome-shaped upper chamber 402 continuous with the upper end of the body 401, and an inverted dome-shaped lower chamber 403 continuous with the lower end of the body 401. The internal space of the body 401 and the internal space of the upper chamber 402 are partitioned by a partition wall 404 and are separated from each other. Similarly, the internal space of the body 401 and the internal space of the lower chamber 403 are partitioned by a partition wall 405 and are separated from each other.

[0036] An opening 41 that communicates between the inside and outside of upper chamber 402 is formed in the wall portion of upper chamber 402. As described above, this opening 41 is connected to opening 11 of polymerization tank 10 via pipe L1 or to opening 22 of concentration tank 20 via pipe L4. Therefore, gas containing a hydrogel-like polymer is introduced into upper chamber 402 from polymerization tank 10 or concentration tank 20 via opening 41.

[0037] A large number of pipes 60 are arranged in the body 401, each extending vertically in an elongated manner. These pipes 60 each extend between a large number of openings formed in the upper partition wall 404 and a large number of openings formed in the lower partition wall 405. Thus, the upper chamber 402 is arranged above the large number of pipes 60, and communicates with the openings at the upper ends of the large number of pipes 60. The lower chamber 403 is arranged below the large number of pipes 60, and communicates with the openings at the lower ends of the large number of pipes 60.

[0038] Each of the multiple pipes 60 defines an elongated passage. The gas sent from the polymerization tank 10 or the concentration tank 20 is introduced into the upper chamber 402, and then introduced from the upper chamber 402 into these passages. The gas dissipates heat while passing through these passages, and is cooled, thereby condensing into a cooling fluid containing liquid and gas. The cooling fluid is then introduced into the lower chamber 403.

[0039] An opening 42 that connects the inside and outside of the lower chamber 403 is formed at the bottom thereof. As described above, this opening 42 is connected to the opening 12 of the polymerization tank 10 via the pipe L2, or to the opening 23 of the concentration tank 20 via the pipe L5. Therefore, the cooling fluid is discharged from the lower chamber 403 to the polymerization tank 10 or the concentration tank 20 via the opening 42.

[0040] Openings 43 and 44 that communicate between the inside and outside of the body 401 are formed in the wall of the body 401. These openings 43 and 44 are arranged separately in the upper and lower parts of the body 401. Furthermore, a number of guide plates 45 are arranged at predetermined intervals in the vertical direction inside the body 401. A number of openings are formed in the guide plates 45, and a number of pipes 60 are inserted into these openings, respectively.

[0041] One of the openings 43 and 44 serves as an inlet for introducing a heat exchange fluid into the body 401, and the other serves as an outlet for discharging the heat exchange fluid from within the body 401. The type of heat exchange fluid is not particularly limited, but may be, for example, water or air. In the example of FIG. 2, the lower opening 44 serves as an inlet, the upper opening 43 serves as an outlet, and the flow of the heat exchange fluid is indicated by an arrow A1. The heat exchange fluid introduced into the body 401 through the inlet, which is one of the openings 43 and 44, advances toward the outlet, which is the other of the openings 43 and 44, while being guided by a number of guide plates 45 within the body 401 and bending, and is discharged from within the body 401 through the outlet. The heat exchange fluid comes into contact with a number of pipes 60 while flowing from the inlet to the outlet within the body 401, and therefore efficient heat exchange is realized between the heat exchange fluid and the gas flowing within the pipes 60, and condensation of the gas is promoted.

[0042] As described above, the gas sent to the heat exchanger 4 contains polymers. If the polymers excessively enter and adhere to the inside of the piping 60 of the heat exchanger 4, causing the piping 60 to become clogged, it will be necessary to periodically stop the operation of the heat exchanger 4, disassemble it, and clean the inside, which is a complicated task. In this embodiment, in order to effectively prevent the piping 60 from being clogged, a cleaning machine 7 is disposed in the upper chamber 402. The cleaning machine 7 is a device that cleans the inside of the heat exchanger 4 (mainly the inside of the upper chamber 402) by spraying a cleaning liquid in the upper chamber 402.

[0043] Incidentally, the present inventors have found that clogging of pipe 60 is more likely to occur when a polymer adheres to the inner wall surface (particularly the top surface) of upper chamber 402 than when the polymer adheres directly to the inner wall surface of pipe 60. In other words, if a polymer adheres to the inner wall surface, particularly the top surface, of upper chamber 402 and grows into a large mass, when this mass subsequently falls off, it will clog pipe 60. The same can be said about the case where a polymer adheres to the top surface of upper partition wall 404.

[0044] From the above, the inventors have discovered that cleaning the inside of upper chamber 402, and more preferably spraying a cleaning liquid at least toward the inner wall surface of upper chamber 402 (cleaning the inner wall surface), is effective in preventing clogging of piping 60. Note that the inside of upper chamber 402 refers to a surface that defines the internal space of upper chamber 402, and in this embodiment, refers to a surface that includes the inner wall surface of upper chamber 402 and the upper surface of upper partition wall 404.

[0045] The inventors have also discovered that it is preferable that the inner wall surface of the upper chamber 402 to be cleaned includes at least the top surface, and further discovered that by cleaning not only the inside of the upper chamber 402 (preferably the inner wall surface of the upper chamber 402, more preferably the top surface included in the inner wall surface of the upper chamber 402) but also the inside of the piping 60, clogging of the piping 60 can be prevented more effectively. In this regard, the cleaning device 7 of the present embodiment can effectively clean not only the inner wall surfaces including the top surface of the upper chamber 402 and the upper surface of the upper partition wall 404, but also the inside of the piping 60.

[0046] The cleaner 7 has a nozzle 70, a first shaft 71 extending in the vertical direction, a second shaft 72 extending in the horizontal direction, a first motor 73 that rotates the first shaft 71, and a second motor 74 that rotates the second shaft 72. The first motor 73 is fixed to the center of the top surface of the upper chamber 402 in a plan view, rotatably receives an upper portion of the first shaft 71, and rotates the first shaft 71 around an axis parallel to the vertical direction. The second motor 74 is fixed to a lower portion of the first shaft 71, rotatably receives one end of the second shaft 72, and rotates the second shaft 72 around an axis parallel to the horizontal direction. The nozzle 70 is fixed to the other end of the second shaft 72.

[0047] In this embodiment, the nozzle 70 is disposed in the upper chamber 402 and has two ejection ports 701 and 702. Both of these ejection ports 701 and 702 open in a direction intersecting (orthogonal in this embodiment) the second axis 72. Moreover, these ejection ports 701 and 702 are disposed at positions 180° apart from each other with respect to the second axis 72, and open in opposite directions. The first motor 73 and the second motor 74 are connected to the control device 5, and the driving of the first motor 73 and the second motor 74, i.e., the rotational operation of the first axis 71 and the second axis 72, is controlled by the control device 5.

[0048] When a cleaning process for cleaning the inside of the heat exchanger 4 is performed, the control device 5 simultaneously drives the first motor 73 and the second motor 74. As a result, the nozzles 701 and 702 included in the nozzle 70 rotate around the second shaft 72 while rotating around the first shaft 71. Hereinafter, the rotation around the first shaft 71 may be referred to as "revolution," and the rotation around the second shaft 72 may be referred to as "rotation."

[0049] 2, a passage through which the cleaning liquid flows is formed inside the first shaft 71 and the second shaft 72. In the cleaning process, the cleaning liquid is supplied from a pump (not shown) into this passage, flows into the nozzle 70, and is sprayed through the nozzles 701 and 702. This pump is connected to the control device 5, which controls the timing and pressure of the cleaning liquid discharge. The type of cleaning liquid is not particularly limited, but is preferably water.

[0050] As described above, in the cleaning step, the nozzles 701 and 702 rotate while revolving, and spray the cleaning liquid during this time. As a result, in the upper chamber 402, the cleaning liquid is sprayed three-dimensionally in all possible directions from the nozzles 701 and 702. The cleaning liquid is sprayed toward the entire surface of the inner wall of the upper chamber 402, including the top and side surfaces, and collides with the entire surface, thereby removing the polymer adhered to the entire surface. The cleaning liquid is also sprayed below the nozzle 70, i.e., toward the upper surface of the upper partition wall 404 and into the pipe 60, and can also remove the polymer adhered to the upper surface of the upper partition wall 404 and the inner wall surface of the pipe 60.

[0051] The lower limit of the flow rate of the cleaning liquid is preferably 50 L / min, more preferably 60 L / min, and even more preferably 70 L / min. The upper limit of the flow rate of the cleaning liquid is preferably 250 L / min, more preferably 200 L / min, and even more preferably 180 L / min. The lower limit of the discharge pressure of the cleaning liquid is preferably 0.2 MPaG, more preferably 3.0 MPaG, and even more preferably 5.0 MPaG. The upper limit of the discharge pressure of the cleaning liquid is preferably 15 MPaG, more preferably 10 MPaG, and even more preferably 8 MPaG. If the flow rate and discharge pressure of the cleaning liquid are within the above ranges, the amount of cleaning liquid used can be effectively reduced, while efficiently crushing and dropping off the polymer lumps adhering to the inside of the upper chamber 402.

[0052] <3. Method for producing water-absorbent resin> A method for producing a water-absorbent resin using the above-mentioned production apparatus 100 will be described below, taking a reversed-phase suspension polymerization method as an example.

[0053] Each step during the production of the water-absorbent resin using the production apparatus 100 is mainly controlled by the control device 5. First, a monomer as a raw material of the water-absorbent resin and a liquid component (hydrocarbon dispersion medium) are accommodated in the polymerization tank 10. The control device 5 drives the agitator and the heater included in the polymerization tank 1 while opening the valves V1 and V2 and communicating the polymerization tank 10 with the inside of the heat exchanger 4A. As a result, the polymerization reaction proceeds in the polymerization tank 10, and a gas containing a hydrogel-like polymer heated by the heat of polymerization is sent to the heat exchanger 4A through the pipe L1. The gas passes through the upper chamber 402 of the heat exchanger 4A, is cooled while passing through the pipe 60, becomes a cooling fluid, and is returned to the polymerization tank 10 through the pipe L2. In this manner, a slurry containing a hydrogel-like polymer is produced in the polymerization tank 10.

[0054] When the treatment in the polymerization vessel 1 is completed, the control device 5 stops the drive of the agitator and the heater included in the polymerization vessel 1 and opens the valve V3. As a result, the slurry in the polymerization vessel 10 is sent to the concentration vessel 20. The control device 5 returns the valve V3 to a closed state after all the slurry in the polymerization vessel 10 is sent to the concentration vessel 20. Furthermore, the control device 5 opens the valves V4 and V5, and drives the agitator and the heater included in the concentrator 2 while the concentration vessel 20 and the heat exchanger 4B are in communication with each other. As a result, the concentration of the slurry progresses in the concentration vessel 20, and the gas containing the heated hydrogel-like polymer is sent to the heat exchanger 4B through the pipe L4. The gas passes through the upper chamber 402 of the heat exchanger 4B, and is cooled while passing through the pipe 60, and becomes a cooling fluid, and the oily component contained in the cooling fluid is returned to the concentration vessel 20 through the pipe L5. In this manner, a concentrated liquid of the slurry is produced in the concentration vessel 20.

[0055] When the treatment in the concentrator 2 is completed, the control device 5 stops driving the agitator and heating device included in the concentrator 2, and opens the valve V6. This causes the concentrated liquid in the concentration tank 20 to be sent to the drying chamber 30. After all of the concentrated liquid in the concentration tank 20 has been sent to the drying chamber 30, the control device 5 returns the valve V6 to a closed state. Furthermore, the control device 5 drives the heating device included in the dryer 3. This causes the polymer contained in the concentrated liquid to be dried in the drying chamber 30. In this manner, a dried water absorbent resin is produced in the drying chamber 30.

[0056] After the treatment in the polymerization vessel 1 is completed, a cleaning process for the inside of the heat exchanger 4A is performed in parallel with the subsequent concentration or drying treatment, or after the completion of these treatments. The control device 5 simultaneously drives the first motor 73, the second motor 74, and the pump included in the cleaning device 7, and while revolving and rotating the nozzle 70 in the upper chamber 402, the cleaning liquid is sprayed from the nozzles 701 and 702, thereby cleaning the inside of the upper chamber 402 and the inside of the piping 60. At this time, with the revolution and rotation of the nozzle 70, the cleaning liquid sprayed from the nozzles 701 and 702 is directly and vigorously sprayed onto the entire inner wall surface including the top surface and side surface of the upper chamber 402 and onto the upper surface of the upper partition wall 404, and the water pressure removes the polymer adhering to the inner wall surface of the upper chamber 402 and the upper surface of the upper partition wall 404. As a result, the polymer lumps adhering to the inside of the upper chamber 402 are crushed and dropped from the inside of the upper chamber 402.

[0057] Similarly, as the nozzle 70 revolves and rotates, the cleaning liquid sprayed from the nozzles 701 and 702 is also sprayed directly and vigorously onto the inside of the pipe 60, and the water pressure removes the polymer adhering to the inner wall surface of the pipe 60. As a result, the polymer lumps adhering to the inner wall surface of the pipe 60 are also crushed and fall off from the inner wall surface of the pipe 60. As a result, the polymer is removed from the inside of the upper chamber 402 and the inside of the pipe 60, and the removed polymer passes through the pipe 60 together with the cleaning liquid, and is recovered in the lower chamber 403. The cleaning liquid containing the polymer recovered in the lower chamber 403 is appropriately discharged outside the system via the opening 42.

[0058] After the treatment in the concentrator 2 is completed, a cleaning process is performed on the inside of the heat exchanger 4B in parallel with the subsequent drying process or after the drying process is completed. This cleaning process is performed in the same manner as the above-mentioned cleaning process on the inside of the heat exchanger 4A, so a detailed description thereof will be omitted here.

[0059] In the above-mentioned washing process, the polymer adhering to the inside of the pipe 60 and the inside of the upper chamber 402 can be effectively removed. As a result, clogging of the pipe 60 can be effectively prevented. In addition, as a result, the water absorbent resin can be efficiently produced.

[0060] <4. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the following modifications are possible.

[0061] <4-1> The first axis 71 does not have to extend in the vertical direction, and the second axis 72 does not have to extend in the horizontal direction. In addition, from the viewpoint of spraying the cleaning liquid in various directions, it is preferable that the first axis 71 and the second axis 72 intersect, but they do not have to be perpendicular to each other.

[0062] <4-2> In the above embodiment, the nozzle 70 of the cleaner 7 is driven by an electric current, but may be driven by a water current.

[0063] <4-3> In the above embodiment, the cleaning liquid is sprayed from the nozzle 70 directly onto both the inside of the pipe 60 and the inside of the upper chamber 402 (the inner wall surface of the upper chamber 402 and the upper surface of the upper partition wall 404), thereby removing the polymer adhering to both. However, the cleaning liquid may be sprayed from the nozzle 70 directly onto only the inside of the upper chamber 402, thereby removing the polymer adhering thereto. In addition, the inside of the upper chamber 402 to be cleaned does not have to include the top surface of the upper chamber 402. In other words, the inside of the upper chamber 402 to be cleaned may be only the side surface of the upper chamber 402, only the upper surface of the upper partition wall 404, or only both.

[0064] For example, by attaching a shower nozzle to the ceiling of upper chamber 402 and spraying cleaning liquid downward from this, it is possible to clean the inside of pipe 60 and the upper surface of upper partition wall 404. In addition, by adjusting the flow rate, discharge pressure, and spray angle of the cleaning liquid sprayed from the shower nozzle, it is possible to further clean the side surfaces included in the inner wall surface of upper chamber 402. The cleaning device 7 used in the above embodiment can also be used in combination with this shower nozzle. EXAMPLES

[0065] Hereinafter, examples 1 and 2 of the present invention will be described, however, the present invention is not limited to the following examples 1 and 2.

[0066] <Example 1> A manufacturing apparatus similar to the manufacturing apparatus 100 according to the above embodiment was prepared, and the water-absorbing resin was manufactured by the manufacturing method according to the above embodiment using the manufacturing apparatus. That is, a series of steps of polymerizing a monomer in a polymerization vessel and then discharging all the slurry into a concentrator was carried out about 350 times. In addition, a washing step of the heat exchanger connected to the polymerization vessel was carried out every time the slurry was discharged into the concentrator. However, among the above 350 steps, the washing step was stopped for the 168th to 243rd steps. In the washing step, the flow rate of the washing liquid was set to 73 L / min, and the discharge pressure of the washing liquid was set to 6.3 MPaG. As a washing machine, a water flow-driven device (automatic rotating nozzle unit "JRN-080PG" manufactured by Sugino Machine Co., Ltd.) was used.

[0067] The pressure inside the polymerization tank and the heat exchanger connected thereto during the above polymerization reaction was measured by a pressure gauge installed inside the polymerization tank. The measurement results of the pressure (maximum pressure during the polymerization reaction) are shown in Figure 3. The horizontal axis of Figure 3 represents the number of times a series of steps were performed, including the polymerization step, the subsequent slurry discharge step, and the heat exchanger cleaning step. The figure also shows the period during which the cleaning step was stopped.

[0068] When the pipes of the heat exchanger are clogged, the pressure inside the polymerization tank and the heat exchanger connected thereto rises. Therefore, it can be said that the pressure in FIG. 3 indicates the cleaning state of the heat exchanger. As can be seen from the above results, the pressure did not rise significantly even after 350 polymerization steps. In addition, when the cleaning step was stopped, the pressure rose, and when the cleaning step was then performed, the pressure dropped again. From the above, the high cleaning effect of the cleaning step according to Example 1 was confirmed.

[0069] <Example 2> In the production apparatus according to Example 1, the cleaning device in the heat exchanger connected to the polymerization vessel was removed, and instead, as described in the above modification 4-3, a shower nozzle ("JJXP150" nozzle manufactured by Kiri no Ikeuchi Co., Ltd.) that sprays the cleaning liquid downward was attached to the top surface of the upper chamber. Then, using this production apparatus, a series of steps of polymerizing the monomer in the polymerization vessel and then discharging all the slurry into the concentrator was carried out about 350 times, as in Example 1. In addition, a cleaning step of the heat exchanger connected to the polymerization vessel was carried out every time the slurry was discharged into the concentrator. In the cleaning step, the flow rate of the cleaning liquid was set to 167 L / min, and the discharge pressure of the cleaning liquid was set to 0.3 MPaG.

[0070] The internal pressures (maximum pressures during the polymerization reaction) in the polymerization tank and in the heat exchanger connected thereto during the polymerization reaction were measured with a pressure gauge installed in the polymerization tank, and the results are shown in Figure 4. The horizontal axis of Figure 4 also represents the number of times a series of steps were performed, including the polymerization step, the subsequent slurry discharge step, and the heat exchanger cleaning step.

[0071] As can be seen from the above results, even after 200 or more polymerization steps, the pressure did not increase significantly. Also, normally, when the pressure reaches about 30 kPaG to 40 kPaG, the heat exchanger may need to be disassembled for cleaning, but even after 300 or more polymerization steps, the pressure was below this standard value. From the above, it was confirmed that the cleaning effect of the cleaning step of Example 2, in which the top surface of the upper chamber was not cleaned, was also high, although it was not as high as that of Example 1, in which the top surface of the upper chamber was cleaned. [Explanation of symbols]

[0072] 100 Water-absorbent resin manufacturing equipment 1 Polymerization vessel 10 Polymerization tank 2 Concentrator 20 Concentrator 3 Dryer 30 Drying room 4(4A, 4B) Heat exchanger 40 Casing 401 Torso 402 Upper Chamber 403 Lower Chamber 60 Piping 7. Cleaning Machine 70 Nozzles 701, 702 spout 71 1st axis 72 2nd axis 73 First Motor 74 Second Motor

Claims

1. A method for producing a water-absorbent resin, comprising the steps of: a cleaning step of cleaning the inside of a heat exchanger that is connected to a container that contains a hydrogel-like polymer that is a precursor of the water-absorbent resin and that cools a gas containing the polymer that is generated in the container; The heat exchanger includes: A number of pipes having elongated passages through which the gas passes, the pipes being configured to be cooled by dissipating heat as the gas passes through the passages; a chamber disposed above the plurality of pipes and communicating with the upper end openings of the plurality of pipes; a cleaning machine that sprays a cleaning liquid into the chamber; The cleaning step includes cleaning at least the inside of the chamber by spraying the cleaning liquid from the cleaner inside the chamber. A method for producing a water-absorbent resin.

2. The method for producing a water-absorbent resin according to claim 1 , wherein the cleaning machine is configured to spray the cleaning liquid toward at least an inner wall surface of the chamber.

3. The method for producing a water-absorbent resin according to claim 2 , wherein the cleaning machine is configured to spray the cleaning liquid toward at least a top surface included in the inner wall surface of the chamber.

4. 4. The method for producing a water-absorbent resin according to claim 1, wherein the cleaning machine rotates around a first axis extending in a first direction while rotating around a second axis extending in a second direction intersecting the first direction, and has an injection port configured to inject the cleaning liquid while rotating around the first axis and the second axis.

5. The container is a polymerization tank for polymerizing a monomer that is a raw material for the water absorbent resin. A method for producing the water-absorbing resin according to any one of claims 1 to 4.

6. the cleaning step includes removing the polymer lumps adhering to at least one of an inner wall surface of the chamber and an inner wall surface of the pipe by spraying the cleaning liquid from the cleaning machine inside the chamber; A method for producing the water-absorbing resin according to any one of claims 1 to 5.

7. the cleaning step includes spraying the cleaning liquid toward the inner wall surface of the chamber to break up and drop off the polymer clumps adhering to the inner wall surface; The method for producing the water-absorbent resin according to claim 6.

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