Abstract:
To provide a solution conveying and cooling apparatus that enables removal of a deposit of solid material, or a fouling deposit, inside the apparatus with extremely simple work equipment by fewer on-site workers in a short tune without any dangerous work such as hydroblasting. The solution conveying and cooling apparatus has a rigid outer tube for a cooling medium and a plurality of rigid outer tubes for solution arranged parallel to each other inside the rigid outer tube for a cooling medium. A thin inner tube is disposed inside each of the rigid outer tubes for solution, this thin inner tube having an outer diameter smaller than an inner diameter of the rigid outer tube for solution at normal temperature and pressure, and expanding by an increase in at least one of temperature and pressure of a solution conveyed and as a result contacting with an inner surface of the rigid outer tube for solution that is cooled by the cooling medium.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a solution conveying and cooling apparatus. 
         [0002]    More specifically, the present invention relates to a solution conveying and cooling apparatus that can readily and efficiently remove polymer fouling and the like that occurs in the production of polymer products such as polyethylene, and polypropylene. Polymer fouling is a deposit of polymer that forms on the inner wall of a polymer reactor which produces polyethylene by, for example, causing a reaction between a catalyst and ethylene in a solvent such as normal hexane, or, a deposit of polymer that accumulates on the inner wall of conveying means for cooling and conveying a liquid mixture of a solvent and a polymer product from the polymer reactor to an after treatment apparatus such as a pelletizer. 
       BACKGROUND ART 
       [0003]    In the polymerization of polyethylene or the like, reaction heat is generated by the polymerization reaction inside the polymer reactor. This reaction heat must be efficiently removed, i.e., cooled, otherwise the operating conditions will be uncontrollable, which may cause significant changes in the physical properties of the polymerization reaction material and in some cases the operation of the polymer reactor may have to be stopped. 
         [0004]    In order to remove the reaction heat, a shell and tube heat exchanger is sometimes installed in conveying means for cooling and conveyance from the inner wall of the polymer reactor and the polymer reactor to an after treatment apparatus such as a pelletizer. In this case, a polymer fouling deposit forms on the inner wall of the metal tube that separates a cooling medium from the polymer contained in the solvent. Since the polymer fouling deposit has a heat conductivity that is lower by about two digits than that of the metal tube, such polymer fouling deposits significantly reduce the efficiency of removal of the reaction heat, i.e., the cooling efficiency. At the same time, the load of the transfer pump will increase, as the pipe diameter is substantially reduced, which may cause adverse effects such as damage or flow rate reduction of the transfer pump. 
         [0005]    Various propositions for preventing an increase in such polymer fouling include:
       (1) Raising the flow speed inside the reactor and conveyor tubes;   (2) Reducing surface roughness of the reactor and conveyor tubes as much as possible;   (3) Adding an anti-electrostatic agent, based on a theory that electrostatic adhesion of catalyst and polymer particles causes the polymer fouling to start;   (4) Improving the structure of the ethylene feed nozzle; and   (5) Improving the structure for preventing a convection flow of polymer through gaps or the like at flanges (see, for example, Non Patent Literature 1).       
 
         [0011]    A method has been proposed as one conventional technique for preventing polymer fouling, in which an anti-fouling agent is added, the agent containing a polyoxyethylene polymer having a number average molecular weight expressed by a specific general formula of not more than 30000, to a component of a solution of a solvent and polymer inside a polymerization apparatus or in a process afterwards (see, for example, Patent Literature 1). 
         [0012]    Another method has been proposed as another conventional technique for preventing polymer fouling, which is a method for enabling continuous operation of an olefin polymerizer by preventing plugging in the system of feeding a catalyst slurry to the polymerization reactor. In the olefin polymerization method, a 0.3 to 3.0 mg organic aluminum compound is entrained in a catalyst slurry containing a preliminary polymerization catalyst carried on a solid per 1 g of this preliminary polymerization catalyst when feeding the catalyst slurry to a gas-phase reactor where main polymerization of olefin takes place (see, for example, Patent Literature 2). 
         [0013]    As another conventional technique for preventing polymer fouling, a heat transfer device  10  has been proposed, which has an inner surface and an outer surface, and is provided for heating or cooling a process stream. The heat transfer device  10  is a tube made of a steel alloy containing three layers of X, Y, and Z. In order to impart corrosion resistance and corrosion-induced fouling resistance to the metal tube heat exchanger that is exposed to the high-temperature process stream, the tube—the heat transfer device  10 —includes three layers, which are a base layer formed from a steel alloy having a surface roughness Ra of less than 40 micro inch (1.1 μm), a Cr-enriched oxide layer containing 10 to 40 wt % chromium formed on at least one of the inner surface and outer surface, and a surface protection layer containing sulfide, oxide, oxysulfide, and mixtures thereof and formed on the surface of the Cr-enriched oxide layer (see, for example, Patent Literature 3). 
         [0014]    Since the formation of polymer fouling cannot be prevented or reduced effectively enough to satisfy industrial demands even with the techniques described above, other methods and techniques have been proposed, one of which is to form a thin film by deposition on the inner wall of a metal tube, the thin film being removable by a solution or gas selected as required (see, for example, Patent Literature 4). 
         [0015]    As another technique for preventing formation of polymer fouling, a de-scaling method has been proposed, in which a resin film is formed on the inner wall of a container where chemical or physical operations are performed, and scales formed on the container inner wall during these operations are removed together with the resin film (see, for example, Patent Literature 5). 
         [0016]    As yet another technique for preventing formation of polymer fouling, an inner tube installation method for a piping system has been proposed, wherein a tube is set inside a pipe for conveying a fluid material that may be a liquid or a paste. The tube is passed through the pipe, and inflated by introducing air into the tube from one end, with the other end being closed, to make tight contact with the pipe, after which both ends of the tube are tightly attached to the ends of the pipe from the inside of the tube (see, for example, Patent Literature 6). 
       CITATION LIST 
     Non Patent Literature 
       [0017]    [NPL 1] “Textbook of Polyethylene Technology” written and edited by Kazuo Matsuura and Naotaka Mikami, published on Jul. 1, 2001 by Kogyo Chosakai Publishing Co., Ltd. 
       PATENT LITERATURE 
       [0018]    [PTL 1] Japanese Patent No. 5399478 
         [0019]    [PTL 2] Japanese Patent Application Laid-open No. 2010-006988 
         [0020]    [PTL 3] Japanese Patent Application Laid-open No. 2013-011437 
         [0021]    [PTL 4] Japanese Patent Application Laid-open No. H10-204668 
         [0022]    [PTL 5] Japanese Patent Application Laid-open No. H05-093001 
         [0023]    [PTL 6] Japanese Patent Application Laid-open No. 2012-232512 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0024]    It is considered that polymer fouling can be removed, as shown in Non Patent Literature 1, physically by passing the fluid at high speed, or by forming a protection layer on the contact surfaces, or by preventing formation of stagnation points, or chemically by adding an anti-electrostatic agent, or the like. 
         [0025]    In actuality, however, none of the countermeasures against polymer fouling disclosed in the patents mentioned above is satisfactory, and reduction in the cooling efficiency due to the polymer fouling, and reduction in the flow passage diameter, i.e., reduction in the flow rate, due to the polymer fouling continue to be a great hindrance in the industrial fields. 
         [0026]    The techniques proposed in Patent Literatures 4 and 5 entail an issue that would be unacceptable in respect of quality control, since it is highly possible that the thin film or resin film formed in advance on the inner wall may dissolve or peel off due to changes in operating conditions or the like and mix in the newly produced polymer. 
         [0027]    The technique proposed in Patent Literature 6 is assumed to be practically impossible to industrially carry out since it would be extremely difficult to mount the flexible inner tube that is stored in a coiled state into each of a bundle of cylindrical tubes of a conveying apparatus, which may have a total length of, for example, about 10 m. 
         [0028]    In a polymer conveying and cooling apparatus determined by the present inventors as an actual example of a case where polymer fouling will occur, a tube bundle is formed by about 1500 cylindrical tubes made of SUS 304 and fixed at equal distance within a circular cross section of 170 cm diameter, each tube having an outer diameter of 25.4 mm, a thickness of 1.2 mm, and a length of 10 m. 
         [0029]    This tube bundle is mounted entirely inside a pressure resistant shell, and a cooling medium is introduced under pressure from an inlet in a lower part in the shell to cause the cooling medium to flow between the bundled tubes. The cooling medium flows around each cylindrical tube and cools the liquid mixture of a solvent and a polymer inside each cylindrical tube. 
         [0030]    Polymers are oversaturated by being cooled and separated from the solvent by precipitation, part of which deposits and grows on the tube wall and forms fouling. As a result, the flow rate of the constant pressure pump is reduced because of the reduction in the flow passage area of the cylindrical tube in which the liquid/solid mixture flows, whereupon normal operation is no longer possible. 
         [0031]    This polymer conveying and cooling apparatus is a pressure vessel and regular inspections are made obligatory by regulations. 
         [0032]    The polymer solution conveying and cooling apparatus described above is normally operated continuously for 24 hours. In this case, deposits of polymer fouling that precipitate and accumulate on the inner walls of cylindrical tubes will have exponentially increased after about 6 months to one year and will significantly hinder the flow of the polymer product solution. As a result, the discharge amount of the constant pressure pump will reduce and normal operation conditions can no longer be achieved, so the cooling apparatus must be stopped to remove the polymer fouling. 
         [0033]    Such work of removing the polymer fouling in a polymer conveying apparatus, which is inevitable with conventional techniques, is achieved by hydroblasting in most industrial applications. 
         [0034]    In hydroblasting, water pressurized by a reciprocating pump is propelled from a nozzle to peel off, pulverize, and discharge or remove the deposits of polymer fouling with the power of impact of the water jet. 
         [0035]    The pressure of hydroblasting is as high as from 7 MPa to 30 MPa, as very high as from 30 MPa to 100 MPa, and sometimes as extremely high as from 100 MPa to 250 MPa. According to “Guidelines on industrial cleaning (hydrocleaning) safety sanitation management” issued by JAPAN WASH INC. Association, hydroblasting must be carried out before a supervisor by a worker who has a specified official approval, and a sturdy scaffold must be built for the work. 
         [0036]    The cleaning of one polymer conveying and cleaning apparatus can take more than two weeks from the setup of the scaffold or the like until the end of the inspection. Moreover, the polymer production has to be stopped during the hydroblasting, which means a loss of revenue due to plant downtime, and therefore such cleaning is a hindrance that can greatly affect industrial activities. 
       Objects of the Invention 
       [0037]    The present invention was made in consideration of the problems described above associated with solution conveying and cooling apparatuses in polymer manufacturing lines and the like that have not been resolved yet by any of the conventional techniques. An object of the present invention is to provide a solution conveying and cooling apparatus that enables removal of a deposit of solid material, or a fouling deposit, inside the apparatus with very simple work equipment as compared to conventional techniques by few on-site workers in a short time without any dangerous work such as hydroblasting. 
         [0038]    Another object of the present invention is to provide a solution conveying and cooling apparatus that reduces the possibility of unwanted deposits on tubes such as polymer being mixed in a solution such as a produced mixture of a liquid and a solid. 
         [0039]    A further object of the present invention is to provide a solution conveying and cooling apparatus that produces a significantly reduced amount of industrial waste as compared to the amount of industrial waste produced by conventional hydroblasting techniques. 
       Solution to Problem 
       [0040]    The present invention resides in 
         [0041]    a solution conveying and cooling apparatus including a rigid outer tube for a cooling medium and a plurality of rigid outer tubes for solution arranged parallel to each other inside the rigid outer tube for a cooling medium, the solution conveying and cooling apparatus being characterized in that 
         [0042]    a thin inner tube is disposed inside each of the rigid outer tubes for solution, this thin inner tube having an outer diameter smaller than an inner diameter of the rigid outer tube for solution at normal temperature and pressure, expanding by an increase in at least one of temperature and pressure of a solution conveyed and, as a result, contacting with an inner surface of the rigid outer tube for solution, and moreover contracting when cooled by the cooling medium or by a pressure drop. 
         [0043]    The present invention also resides in 
         [0044]    a polymer manufacturing apparatus including a polymerization reaction apparatus and a cooling passage (heat exchanger) connected to a polymer product outlet of the polymerization reaction apparatus, the polymer manufacturing apparatus being characterized in that 
         [0045]    the cooling passage includes a liquid/solid mixture conveying apparatus, wherein a plurality of rigid outer tubes are arranged parallel to each other inside a rigid outer tube for a cooling medium, and 
         [0046]    a thin inner tube is disposed inside each of the rigid outer tubes for mixture, this thin inner tube having an outer diameter smaller than an inner diameter of the rigid outer tube for mixture at normal temperature and pressure, expanding by an increase in at least one of temperature and pressure of a solution conveyed and, as a result, contacting with an inner surface of the rigid outer tube for mixture, and moreover contracting when the solution is cooled by the cooling medium or pressure is dropped. 
       Advantageous Effects of Invention 
       [0047]    The liquid conveying and cooling apparatus of the present invention can provide the effect of safe removal of a deposit of solid material such as polymer or the like inside the liquid conveying apparatus with very simple work equipment as compared to conventional techniques by few workers in a short time. 
         [0048]    The solution conveying and cooling apparatus of the present invention can also provide the effect of eliminating the risk of unwanted impurities such as existing polymer or the like that has adhered to the tube inner surface mixing in a fluid being conveyed and cooled such as a solution of newly produced polymer or the like. 
         [0049]    The liquid conveying apparatus of the present invention can also provide the effect of significantly reducing the production of industrial waste as compared to conventional hydroblasting techniques. 
         [0050]    Examples of applications where the liquid conveying apparatus of the present invention may be suitably embodied include: polymerization reaction in the polymer production: chemical operation such as cross-link reaction: and solution conveyance during a process of physical operation such as so desolventizing, mixing, and the like. Other possible applications include solution conveyance or the like during a process of physical operation such as mixing of polymer with other components, desolventizing, and the like in the production or the like of compositions mainly composed of a polymer such as paints, adhesives, and the like. 
         [0051]    The present invention may be applied to conveyance of a solution in the production of polymers such as methacrylate ester polymers such as poly(methyl) methacrylates, poly(ethyl) methacrylates, and poly(butyl) methacrylates, urethane polymers, polyvinyl chlorides, polyvinylidene chlorides, SBR, polyvinyl acetates, or copolymers of monomers constituting these, and can also favorably be applied to conveyance of a solution in the production of emulsions such as urethane emulsions, acrylic emulsions and the like. 
       EMBODIMENTS OF INVENTION 
       [0052]    The present invention is further characterized in that the thin inner tube is made of an SUS300-based stainless steel, an aluminum alloy, a copper alloy, and the like. 
         [0053]    The present invention is further characterized in that the thin inner tube is press-joined to a thin inner tube support disc at an end. 
         [0054]    The present invention is further characterized in that the solution is a solution mixture of a solvent and a polymer product. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0055]      FIG. 1  is a partially cut-open front view of a solution conveying and cooling apparatus of a first embodiment. 
           [0056]      FIG. 2  is a cross-sectional view along line II-II of  FIG. 1 . 
           [0057]      FIG. 3  is an enlarged view of an area encircled with a dot line III in  FIG. 1 . 
           [0058]      FIG. 4  is an illustrative diagram showing how the thin inner tube is fixedly attached to the rigid outer tube for solution. 
           [0059]      FIG. 5  is an illustrative reference diagram for explaining the principle of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0060]    The solution conveying and cooling apparatus of one embodiment of the present invention will now be described with reference to the drawings. Figures in the description of the embodiment are all given as examples. 
         [0061]    The solution conveying and cooling apparatus  1  of the present invention is a shell and tube type apparatus used for a pressure vessel that has a heat exchange function and is used for carrying out low and medium pressure polyethylene polymerization. Three types of shell and tube heat exchangers are known: fixed tube sheet exchangers, floating head exchangers, and U-tube exchangers. The solution conveying and cooling apparatus  1  is a floating head exchanger, which absorbs expansion and contraction of elongated heat exchange tubes caused by high temperature and high pressure of fluid with which heat exchange takes place by displacement of a floating head cover. 
         [0062]    The solution conveying and cooling apparatus  1  has a heat exchanging fluid chamber  14  and a cooling medium chamber  16  formed by partitioning the interior of the body, or a shell  10 , with a tube sheet  12 , as shown in  FIG. 1 . 
         [0063]    The heat exchanging fluid chamber  14  that contains a fluid R with which heat exchange takes place is formed by closing one end of the shell  10  with a shell cover  20 . In the part of the shell  10  where the heat exchanging fluid chamber  14  is located, a heat exchanging fluid inlet  22  is disposed on the lower side, and a heat exchanging fluid outlet  24  is disposed on the upper side. The heat exchanging fluid chamber  14  is divided by a partition  40  into a lower high-temperature part  14   a  and a lower low-temperature part  14   b.    
         [0064]    One example of the heat exchanging fluid R is a mixture of normal hexane and polymer. 
         [0065]    The cooling medium chamber  16  that contains a cooling medium W such as cooling water is formed by closing one end of the shell  10  with a cooling medium chamber cover  30 , and has about 2000 heat exchange tubes  32 , for example, arranged parallel to each other inside. On the opposite side of the tube sheet  12  inside the cooling medium chamber  16  is disposed a floating head cover  34 . Baffle plates  36  are arranged in the cooling medium chamber  16  for agitating the cooling medium W. 
         [0066]    The heat exchange tubes  32  are configured in the solution conveying and cooling apparatus  1  as shown in  FIG. 2 : Rigid outer tubes for mixture  102  made of SUS304 for passing a mixture solution containing a product substance dissolved in a solvent are arranged parallel to each other inside a rigid outer tube for a cooling medium  100  made of iron for passing a cooling medium. 
         [0067]    The rigid outer tube for a cooling medium  102  has a length of 10 m in the cooling medium passage part. As shown in  FIG. 3 , the outer diameter is 25.4 mm, the thickness is 2.0 mm, and the inner diameter is 21.4 mm. 
         [0068]    The rigid outer tubes for solution  102  are fixed by welds  106  to rigid outer tube support plates  104  fixedly attached inside near both ends of the rigid outer tubes for solution  102  as shown in  FIG. 1  and as shown in  FIG. 4 . 
         [0069]    Each of the rigid outer tubes for mixture  102  has a thin inner tube  110  disposed inside as shown in  FIG. 3  and  FIG. 4 . The thin inner tube  110  has an inner diameter of 21.30 mm and a thickness of 0.04 mm. Both ends of the thin inner tube  110  are fixedly attached to the ends of each rigid outer tube for mixture  102  by press-joining as shown in  FIG. 4 . 
         [0070]    Hereinafter, an explanation based on calculations will be given as to how the thin inner tube  110  expands by temperature and pressure of a solution being conveyed, for example a liquid mixture of reaction products and solvent, and makes contact with the inner surface of the rigid outer tube for solution  102  without rupture, and how the thin inner tube  110  contracts in diameter and returns to its original size when pressure is reduced or when the solution is removed, as well as how the thin inner tube  110  is backed up by the rigid outer tube for solution  102 , i.e., how the thin inner tube  110  is supported all around by the rigid outer tube for solution  102 , when it expands by the temperature and pressure of the solution or a mixture of a liquid and a solid being conveyed. 
         [0071]    The hoop stress, or circumferential tensile stress, σ i N/m 2  of the thin inner tube  110  is: 
         [0000]      σ i   =pD 1/2 t 1= PD/ 2 t   (1)
 
         [0000]    when the inner diameter is D mm, the thickness is t mm, the length is 1 mm, and the inner pressure is P Pascal as shown in  FIG. 5 , for example according to a description regarding “tensile stress working in a circumferential direction” in line 8 on page 70 of “Introduction to Material Mechanics” (written by Takashi Arimitsu) published on May 25, 2012 by Gijutsu-Hyohron Co., Ltd. 
         [0072]    The allowable tensile stress of SUS304 is, according to JIS G4303, 194 MPa at 40° C., 180 MPa at 75° C., and 171 MPa at 100° C. 
         [0073]    Taking into consideration that, in the high-temperature part  14   a  and low-temperature part  14   b  of a heat exchanging fluid chamber, which are commonly seen in industrial fields, the temperatures and pressures are 70° C. and 57° C., and 1.20 MPa and 1.14 MPa, respectively, calculation is made using the following figures. 
         [0074]    The thickness of the rigid outer tube for solution  102  is 2.0 mm. The inner diameter of the rigid outer tube for solution  102  is 21.40 mm. The thin inner tube  110  has an outer diameter of 21.37 mm. The thin inner tube  110  has a thickness of 0.04 mm. The internal pressure of the thin inner tube  110  is 1.20 MPa. The Young&#39;s modulus of SUS304 that is the material of the rigid outer tube for solution  102  and the thin inner tube  110  is 200 GPa. 
         [0075]    The clearance or gap between the inner surface of the rigid outer tube for solution  102  and the outer surface of the thin inner tube  110  is 0.015 mm, a half of 0.03 mm. 
         [0000]    (Thin Inner Tube in Tight Contact with the Rigid Outer Tube for Solution) 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       Hoop 
                        
                       
                           
                       
                        
                       stress 
                        
                       
                           
                       
                        
                       
                         σ 
                         i 
                       
                     
                     = 
                       
                      
                     
                       PD 
                        
                       
                         / 
                       
                        
                       2 
                        
                       t 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       
                         ( 
                         
                           1.2 
                            
                           
                               
                           
                            
                           MPa 
                           × 
                           21.30 
                            
                           
                               
                           
                            
                           mm 
                         
                         ) 
                       
                        
                       
                         / 
                       
                        
                       
                         ( 
                         
                           2 
                           × 
                           0.04 
                            
                           
                               
                           
                            
                           mm 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       319.5 
                        
                       
                           
                       
                        
                       
                         ( 
                         MPa 
                         ) 
                       
                     
                   
                 
               
             
               
           
         
       
     
       Based on Hooke&#39;s Law, 
       [0076]    
       
         
           
             
               
                 
                   
                     
                       Strain 
                        
                       
                           
                       
                        
                       ɛ 
                     
                     = 
                       
                      
                     
                       stress 
                        
                       
                           
                       
                        
                       
                         σ 
                         i 
                       
                        
                       
                         / 
                       
                        
                       
                         Young 
                         &#39; 
                       
                        
                       s 
                        
                       
                           
                       
                        
                       module 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       319.5 
                        
                       
                           
                       
                        
                       MPa 
                        
                       
                         / 
                       
                        
                       200 
                        
                       
                           
                       
                        
                       GPa 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       0.0016 
                        
                       
                           
                       
                        
                       
                         ( 
                         
                           0.16 
                            
                           % 
                         
                         ) 
                       
                     
                   
                 
               
             
               
           
         
       
     
         [0077]    Therefore, the outer diameter of the thin inner tube  110  will be increased by the internal pressure by: 
         [0000]      21.37 mm×0.0016=0.034 mm
 
         [0078]    This figure indicates the possibility of the thin inner tube  110  making so tight contact with the rigid outer tube for solution  102  by the internal pressure. 
       (Rigid Outer Tube for Solution Backing Up the Expanding Thin Inner Tube) 
       [0079]    Let us assume that an internal pressure of 1.20 MPa is applied to the rigid outer tube for solution  102 . 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       Hoop 
                        
                       
                           
                       
                        
                       stress 
                        
                       
                           
                       
                        
                       
                         σ 
                         i 
                       
                     
                     = 
                       
                      
                     
                       PD 
                        
                       
                         / 
                       
                        
                       2 
                        
                       t 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       
                         ( 
                         
                           1.2 
                            
                           
                               
                           
                            
                           MPa 
                           × 
                           23.40 
                            
                           
                               
                           
                            
                           mm 
                         
                         ) 
                       
                        
                       
                         / 
                       
                        
                       
                         ( 
                         
                           2 
                           × 
                           2.0 
                            
                           
                               
                           
                            
                           mm 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       7.02 
                        
                       
                           
                       
                        
                       
                         ( 
                         MPa 
                         ) 
                       
                     
                   
                 
               
             
               
           
         
       
     
       Based on Hooke&#39;s Law, 
       [0080]    
       
         
           
             
               
                 
                   
                     
                       Strain 
                        
                       
                           
                       
                        
                       ɛ 
                     
                     = 
                       
                      
                     
                       stress 
                        
                       
                           
                       
                        
                       
                         σ 
                         i 
                       
                        
                       
                         / 
                       
                        
                       
                         Young 
                         &#39; 
                       
                        
                       s 
                        
                       
                           
                       
                        
                       module 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     
                       7.02 
                        
                       
                           
                       
                        
                       MPa 
                        
                       
                         / 
                       
                        
                       200 
                        
                       
                           
                       
                        
                       GPa 
                     
                   
                 
               
               
                 
                   
                     = 
                       
                      
                     0.000 
                   
                 
               
             
               
           
         
       
     
         [0081]    Therefore, even if an internal pressure of 1.20 MPa is applied to the rigid outer tube for solution  102 , the rigid outer tube for solution  102  will hardly expand and can back up the thin inner tube  110 . 
       (Diameter Reduction of Thin Inner Tube) 
       [0082]    The “0.2% proof stress” mentioned in “Research Report by Tokyo Metropolitan Industrial Technology Research Institute, No. 5, 2010” (page 78) and others refers to the residual strain being not more than 0.2% when a certain level of pressure is loaded and removed. According to this paper, SUS304 has a 0.2% proof stress of 314 MPa. That is, the proof stress (314 MPa) of SUS304 is higher than its yield stress. If, in this embodiment, the clearance between the rigid outer tube for solution  102  and the thin inner tube  110  is not more than 0.2%, the residual strain that may be caused by creep and metal fatigue will not exceed 0.2%. If the clearance between the rigid outer tube for solution  102  and the thin inner tube  110  is not more than 0.1%, the thin inner tube  110  will make tight contact with the rigid outer tube for solution  102  and be backed up by the rigid outer tube for solution  102 , and will return to its original size after the pressure is removed. 
         [0083]    Next, how the solution conveying and cooling apparatus  1  of the present invention is used will be described. First, the thin inner tube  110  is inserted into the rigid outer tube for mixture  102 . Since the thin inner tube  110  is as light as, for example, 514 g, and also since there is some space between the inner surface of the rigid outer tube for mixture  102  and the outer surface of the thin inner tube  110 , it can be easily inserted even though it is as long as, for example, 10 m. The inserted thin inner tube  110  may be used as is, but preferably, both ends of the thin inner tube  110  may be fixedly attached to both ends of the rigid outer tube for mixture  102  by press-joining or the like. 
         [0084]    When a polymer product is introduced into the thin inner tube  110  in this state, the thin inner tube  110  expands by the pressure from the polymer product and the entire circumferential surface of the thin inner tube  110  makes contact with the inner circumferential surface of the rigid outer tube for mixture  102 . As a result, the thin inner tube  110  is supported by the inner circumferential surface of the rigid outer tube for mixture  102  all around. Furthermore, as the entire outer circumference of the thin inner tube  110  is in contact with the inner circumferential surface of the rigid outer tube for mixture  102 , the polymer product being conveyed inside the thin inner tube  110  can be efficiently cooled by the cooling medium flowing between the rigid outer tube for mixture  102  and the rigid outer tube for the cooling medium  100 . 
         [0085]    When continuous operation over a long time of the liquid/solid mixture conveying apparatus  1  has led to polymer fouling inside the thin inner tube  110 , the flow of polymer product into the liquid/solid mixture conveying apparatus  1  is stopped. As the pressure returns to normal, the thin inner tube  110  reduces in diameter and returns to its size. As a result, a space is formed between the inner circumferential surface of the rigid outer tube for mixture  102  and the outer circumferential surface of the thin inner tube  110 , so that the thin inner tube  110  can be easily taken out from the rigid outer tube for mixture  102 . 
         [0086]    The removed thin inner tube  110  is then subjected to a polymer fouling removal process in a place more suited for the operation such as a plant. The thin inner tube  110  after being cleared of the polymer fouling is inserted into the rigid outer tube for mixture  102  by the method described above. 
         [0087]    Preparing a spare thin inner tube  110  and replacing the thin inner tube  110  with polymer fouling with this spare thin inner tube  110  enables a safe operation of removing polymer fouling in high places in a short period of time and is very effective for improving the production efficiency of the polymer. 
       INDUSTRIAL APPLICABILITY 
       [0088]    The present invention can be carried out also in applications where pressure only varies and there are no large temperature changes as would be in pipes for pumping mineral oil from under the ground, and can eliminate the plugging efficiently. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Solution conveying and cooling apparatus 
           100  Rigid outer tube for a cooling medium 
           102  Rigid outer tube for solution 
           104  Support plate for rigid outer tube for solution 
           106  Weld 
           110  Thin inner tube