SOLUTION CONVEYING AND COOLING APPARATUS

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.

Claims

1. A solution conveying and cooling apparatus having 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 apparatus being characterized in that a thin inner tube is disposed inside each of said rigid outer tubes for solution, said thin inner tube having an outer diameter smaller than an inner diameter of said 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 said rigid outer tube for solution, and moreover contracting in diameter, by cooling or pressure drop of said solution.

2. The solution conveying and cooling apparatus according to claim 1, wherein said thin inner tube is made of an SUS300-based stainless steel.

3. The solution conveying and cooling apparatus according to claim 1, wherein said thin inner tube is made of an aluminum alloy.

4. The solution conveying and cooling apparatus according to claim 1, wherein said thin inner tube is made of a copper alloy.

5. The solution conveying and cooling apparatus according to claim 1, wherein said solution is a solution mixture of a solvent and a polymer product.

6. A polymer manufacturing apparatus comprising 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 said cooling passage includes 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, and a thin inner tube is disposed inside each of said rigid outer tubes for solution, said thin inner tube having an outer diameter smaller than an inner diameter of said 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 said rigid outer tube for solution, and moreover contracting in diameter, and moreover contracting in diameter, by cooling or pressure drop of said solution.

7. The polymer manufacturing apparatus according to claim 6, wherein said thin inner tube is made of an SUS300-based stainless steel.

8. The polymer manufacturing apparatus according to claim 6, wherein said thin inner tube is made of an aluminum alloy.

9. The polymer manufacturing apparatus according to claim 6, wherein said thin inner tube is made of a copper alloy.

10. The polymer manufacturing apparatus according to claim 6, wherein said thin inner tube is press-joined, at an end thereof, to said rigid outer tube for solution.

11. The polymer manufacturing apparatus according to claim 6, wherein said solution is a solution mixture of a solvent and a polymer product.

Description

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 14a and a lower low-temperature part 14b.

[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, .sub.iN/m.sup.2 of the thin inner tube 110 is:

.sub.i=pD1/2t1=PD/2t(1)

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 14a and low-temperature part 14b 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'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.

(Thin Inner Tube in Tight Contact with the Rigid Outer Tube for Solution)

[00001]$\begin{array}{c}\mathrm{Hoop}.Math..Math.\mathrm{stress}.Math..Math.{}_i=.Math.\mathrm{PD}.Math.\text{/}.Math.2.Math.t\\ =.Math.\left(1.2.Math..Math.\mathrm{MPa}21.30.Math..Math.\mathrm{mm}\right).Math.\text{/}.Math.\left(20.04.Math..Math.\mathrm{mm}\right)\\ =.Math.319.5.Math..Math.\left(\mathrm{MPa}\right)\end{array}$

Based on Hooke's Law,

[0076] [00002]$\begin{array}{c}\mathrm{Strain}.Math..Math.\mathrm{.Math.}=.Math.\mathrm{stress}.Math..Math.{}_i.Math.\text{/}.Math.\mathrm{Young}\text{'}.Math.s.Math..Math.\mathrm{module}\\ =.Math.319.5.Math..Math.\mathrm{MPa}.Math.\text{/}.Math.200.Math..Math.\mathrm{GPa}\\ =.Math.0.0016.Math..Math.\left(0.16.Math.\%\right)\end{array}$

[0077] Therefore, the outer diameter of the thin inner tube 110 will be increased by the internal pressure by:

21.37 mm0.0016=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.

[00003]$\begin{array}{c}\mathrm{Hoop}.Math..Math.\mathrm{stress}.Math..Math.{}_i=.Math.\mathrm{PD}.Math.\text{/}.Math.2.Math.t\\ =.Math.\left(1.2.Math..Math.\mathrm{MPa}23.40.Math..Math.\mathrm{mm}\right).Math.\text{/}.Math.\left(22.0.Math..Math.\mathrm{mm}\right)\\ =.Math.7.02.Math..Math.\left(\mathrm{MPa}\right)\end{array}$

Based on Hooke's Law,

[0080] [00004]$\begin{array}{c}\mathrm{Strain}.Math..Math.\mathrm{.Math.}=.Math.\mathrm{stress}.Math..Math.{}_i.Math.\text{/}.Math.\mathrm{Young}\text{'}.Math.s.Math..Math.\mathrm{module}\\ =.Math.7.02.Math..Math.\mathrm{MPa}.Math.\text{/}.Math.200.Math..Math.\mathrm{GPa}\\ =.Math.0.000\end{array}$

[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

[0089] 1 Solution conveying and cooling apparatus [0090] 100 Rigid outer tube for a cooling medium [0091] 102 Rigid outer tube for solution [0092] 104 Support plate for rigid outer tube for solution [0093] 106 Weld [0094] 110 Thin inner tube