Method for suppressing blockage of second pipe due to agglomerating powder in gas flowing through first pipe, system for suppressing blockage of second pipe, pipe structure for suppressing blockage of second pipe, and method for producing polyolefin

Abstract

This method suppresses blockage of a second pipe due to agglomerating powder in a gas flowing through a first pipe, wherein the first pipe through which the gas containing agglomerating powder flows, the second pipe that is connected to the first pipe and is provided substantially perpendicular to the first pipe, and a third pipe that is connected to the second pipe and is provided to the second pipe in a plane substantially parallel to the first pipe are provided; the gas containing the agglomerating powder flows in one direction through the first pipe; the second pipe and the third pipe are connected so that an angle formed by the flow direction of the gas flowing through the first pipe and the flow direction of purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; and the method involves supplying the purge gas toward the second pipe through the third pipe at a predetermined flow rate with respect to the gas flow rate flowing through the first pipe.

Description

Method for preventing clogging of second pipe caused by cohesive powder in gas flowing through first pipe, system for preventing clogging of second pipe, piping structure for preventing clogging of second pipe, and method for producing polyolefin

[0001] The present invention relates to a method for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, a system for suppressing clogging of a second pipe, a piping structure for suppressing clogging of a second pipe, and a method for producing polyolefins.

[0002] In the polyolefin production process, as catalyst performance has improved dramatically, the necessity of removing catalyst residues and atactic polymers has decreased, and gas phase processes are now the mainstream.

[0003] Known gas-phase polymerization reactors used in gas-phase processes for producing olefins such as propylene and ethylene include a reactor vessel, which is the main body of the polymerization reactor, and an agitator having a stirring shaft and a stirring blade fixed on the stirring shaft, which is disposed within the reactor vessel as a means for homogenizing a reaction system containing raw material monomers and a catalyst. Patent Document 1 discloses a so-called vertical polymerization reactor in which a cylindrical reactor vessel is installed vertically and an agitator having a stirring shaft that rotates about a vertical axis is disposed within the reactor. Patent Document 2 discloses a so-called horizontal polymerization reactor in which a cylindrical reactor vessel is installed horizontally and an agitator having a stirring shaft that rotates about a horizontal axis is disposed within the reactor.

[0004] JP-A-53-123487 JP-A-63-223001

[0005] In a gas-phase polymerization reactor, unreacted gas is usually discharged outside the reaction system through an unreacted gas extraction pipe and resupplied via a condenser, a compressor, a raw material supply pipe, etc. The gas extracted from the gas-phase polymerization reactor usually inevitably contains fine polyolefin powder. Thus, the gas-phase polymerization reactor is connected to a pipe, such as an unreacted gas extraction pipe, for transferring the gas containing polyolefin powder extracted from the gas-phase polymerization reactor. The pipe (first pipe) for transferring the gas containing polyolefin powder extracted from the gas-phase polymerization reactor is further connected to a pipe (second pipe) communicating with, for example, a pressure gauge, a safety valve, a thermometer, a release valve, a differential pressure gauge, etc. However, since polyolefin powder is a cohesive powder, there is a problem in that the second pipe is clogged by the polyolefin powder in the gas flowing through the first pipe. If the second pipe is clogged, production problems may occur due to poor measurement by the pressure gauge or thermometer, or time-consuming and complicated work such as stopping operation to remove the powder clogged in the pipe is required, making it difficult to stably produce polyolefins over a long period of time. Therefore, there is a need for technological improvements to prevent clogging of the second pipe.

[0006] In view of the above circumstances, the object of the present invention is to provide a method for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, a system for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, a piping structure for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, and a method for producing polyolefins using the method.

[0007] The present inventors have discovered that by connecting a third pipe for flowing a purge gas toward the second pipe to the second pipe in a specific arrangement and by appropriately controlling the flow rate of the purge gas, it is possible to prevent cohesive powder in the gas flowing through the first pipe from entering the second pipe and to prevent clogging of the second pipe, and have arrived at the present invention. That is, the present invention includes the following aspects.

[0008] [1] A method for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through the first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the gas containing the cohesive powder flows in one direction through the first pipe, the second pipe and the third pipe are connected so that an angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°, and the method comprises supplying the purge gas through the third pipe toward the second pipe at a predetermined flow rate with respect to a flow rate of the gas flowing through the first pipe. [2] The method for suppressing clogging of a second pipe according to [1], wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge. [3] The method for suppressing clogging of a second pipe according to [1] or [2], wherein a flow velocity (V1) (m / s) of the gas containing a cohesive powder flowing through the first pipe, a flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and an inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 − 0.33 (1) [4] The method for suppressing clogging of a second pipe according to any one of [1] to [3], wherein the cohesive powder is a polyolefin powder.

[0009] [5] A system for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the second pipe and the third pipe are connected so that an angle formed between a flow direction of the gas flowing through the first pipe and a flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; purge gas supply means for supplying purge gas toward the second pipe through the third pipe; and control means for controlling a flow rate of the purge gas by supplying the purge gas so as to suppress intrusion of the cohesive powder in the gas flowing through the first pipe into the second pipe. [6] The clogging suppression system for a second pipe according to [5], wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge. [7] The clogging suppression system for a second pipe according to [5] or [6], wherein the control means controls the flow rate of the purge gas so that a flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe, a flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and an inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 - 0.33 (1) [8] The clogging suppression system for a second pipe according to any one of [5] to [7], wherein the cohesive powder is a polyolefin powder.

[0010] [9] A piping structure for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed on the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the second pipe and the third pipe are connected so that an angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°.

[10] The piping structure for suppressing clogging of the second pipe according to [9], wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

[11] The piping structure for suppressing clogging of the second pipe according to [9] or

[10] , wherein the cohesive powder is polyolefin powder.

[0011]

[12] A method for producing polyolefins using a polyolefin polymerization apparatus including a gas-phase polymerization reactor and a first pipe for transferring a gas containing polyolefin powder removed from the gas-phase polymerization reactor, wherein the polyolefin polymerization apparatus includes: a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the gas containing polyolefin powder flows in one direction through the first pipe; the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; and the method for producing polyolefins includes supplying the purge gas through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe.

[13] The method for producing a polyolefin according to

[12] above, wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

[14] The method for producing a polyolefin according to

[12] above or

[13] above, wherein a flow velocity (V1) (m / s) of the gas containing polyolefin powder flowing through the first pipe, a flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and an inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 - 0.33 (1)

[0012] According to the present invention, it is possible to provide a method for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, a system for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, a piping structure for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, and a method for producing a polyolefin using the above method.

[0013] FIG. 1 is a schematic perspective view showing an example of a piping structure used in the present invention. FIG. 2 is a schematic cross-sectional view illustrating the piping structure used in the present invention. FIG. 3 is a schematic plan view illustrating the connection direction of the third pipe in the piping structure used in the present invention. FIG. 4 is a schematic explanatory view illustrating an example of the arrangement of a polyolefin polymerization apparatus equipped with a horizontal gas-phase polymerization reactor. FIG. 5 is a schematic explanatory view illustrating an example of the arrangement of a polyolefin polymerization apparatus equipped with a vertical fluidized bed reactor. FIG. 6 is a schematic cross-sectional view illustrating the simulation results of Comparative Example 2. FIG. 7 is a schematic cross-sectional view illustrating the simulation results of Example 2. FIG. 8 is a schematic cross-sectional view illustrating the simulation results of Comparative Example 3. FIG. 9 is a graph showing the purge gas velocity (V3) relative to the reaction gas velocity (V1) in the first pipe and the average reaction gas concentration in the second pipe for the results of a simulation performed under the conditions of Table 1. FIG. 10 is a graph showing the simulation results of the reaction gas concentration under conditions A, B, and C in FIG. 9. 11 is a graph showing the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions of Table 2. FIG. 12 is a graph showing the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions of Table 3. FIG. 13 is a graph showing the correlation between the lower limit of the velocity ratio (V3 / V1) of the purge gas velocity (V3) to the reactant gas velocity (V1) in the first pipe and the inner diameter (D2) (mm) of the second pipe. FIG. 14 is a graph showing the correlation between the lower limit of the velocity ratio (V3 / V1) of the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe. Fig. 15 is a graph showing the correlation between the allowable upper limit of the average reactant gas concentration in the second pipe and the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe. Fig. 16 is a graph showing the relationship between the connection angle θ1 (°) and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions in Table 5.

[0014] The present invention will be described in detail below. The following description of the constituent elements is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the present invention. In this specification, the term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the upper and lower limits. In addition, in this specification, any combination of the upper and lower limits indicating a numerical range can be used. Furthermore, in this specification, any combination of the preferred ranges of each characteristic can be used.

[0015] A first aspect of the present invention is a method for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the gas containing the cohesive powder flows in one direction through the first pipe, the second pipe and the third pipe are connected so that an angle formed between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°, and the method comprises supplying the purge gas through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe.

[0016] A second aspect of the present invention is a system for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, the system comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; purge gas supply means for supplying the purge gas toward the second pipe through the third pipe; and control means for controlling the flow rate of the purge gas by supplying the purge gas so as to suppress intrusion of the cohesive powder in the gas flowing through the first pipe into the second pipe.

[0017] A third aspect of the present invention is a piping structure for suppressing clogging of the second piping by cohesive powder in the gas flowing through the first piping, comprising: a first piping for flowing a gas containing a cohesive powder; a second piping connected to the first piping and arranged substantially perpendicular to the first piping; and a third piping connected to the second piping and arranged on the second piping in a plane substantially parallel to the first piping, for flowing a purge gas, wherein the second piping and the third piping are connected so that the angle between the flow direction of the gas flowing through the first piping and the flow direction of the purge gas flowing through the third piping in a plane substantially parallel to the flow direction of the gas flowing through the first piping is within 30°.

[0018] A fourth aspect of the present invention is a method for producing polyolefins using a polyolefin polymerization apparatus comprising a gas-phase polymerization reactor and a first pipe for transferring a gas containing polyolefin powder removed from the gas-phase polymerization reactor, wherein the polyolefin polymerization apparatus comprises: a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the gas containing polyolefin powder flows in one direction through the first pipe; the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; and the method comprises supplying the purge gas through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe.

[0019] First, we will explain a polyolefin production method to which the method of the present invention for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe is suitable. Conventionally, a second pipe connected to a pipe (first pipe) for transporting a gas containing polyolefin powder extracted from a gas-phase polymerization reactor has a problem of being easily clogged by polyolefin powder in the gas flowing through the first pipe. In contrast, the polyolefin production method of the present invention includes a first pipe for transporting a gas containing polyolefin powder extracted from a gas-phase polymerization reactor, a second pipe connected to the first pipe and arranged substantially perpendicular to the first pipe, and a third pipe for flowing a purge gas is connected to the second pipe in the specific arrangement described above. By supplying a purge gas through the third pipe toward the second pipe at a flow rate predetermined relative to the flow rate of the gas flowing through the first pipe, clogging of the second pipe due to polyolefin powder in the gas flowing through the first pipe can be suppressed. Therefore, the polyolefin production method of the present invention has excellent long-term operational stability.

[0020] In the following description of the polyolefin production method of the present invention, the piping structure for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe and the method for suppressing clogging of the second pipe of the present invention will be described with reference to the drawings. In the following description, since the polyolefin powder in the gas flowing through the first pipe is a cohesive powder, it will be generally described as a cohesive powder.

[0021] Fig. 1 is a schematic perspective view showing an example of a piping structure used in the present invention, and Fig. 2 is a schematic cross-sectional view illustrating the piping structure used in the present invention. As shown in Fig. 1, the piping structure 200 used in the present invention includes a first pipe 101 for flowing a gas containing a cohesive powder, a second pipe 102 connected to the first pipe and arranged substantially perpendicular to the first pipe, and a third pipe 103 connected to the second pipe and arranged in a plane 105 substantially parallel to the first pipe for flowing a purge gas arranged in the second pipe, wherein the second pipe 102 and the third pipe 103 are connected so that the angle between the flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°. Note that in the method for suppressing clogging of a second pipe and the method for producing a polyolefin of the present invention, the gas containing a cohesive powder flows in one direction through the first pipe. Therefore, in the following description, the first pipe may be referred to as "the first pipe through which the gas containing the cohesive powder flows."

[0022] In the present invention, "perpendicular" does not only mean completely perpendicular, but also means a certain degree of inclination from the completely perpendicular, depending on the range that a person skilled in the art would expect to obtain the effects of the present invention or manufacturing reasons. In the present invention, the second pipe 102 arranged perpendicular or substantially perpendicular to the first pipe 101 may be arranged at an angle of ±15° from the completely perpendicular direction with respect to the first pipe 101. Furthermore, the second pipe 102 arranged perpendicular or substantially perpendicular to the first pipe 101 may be arranged at an angle of ±10° from the completely perpendicular direction with respect to the first pipe 101, or may be arranged at an angle of ±5° from the completely perpendicular direction.

[0023] In the present invention, "parallel" does not necessarily mean "perfectly parallel," but also means that the third pipe 103 disposed on the second pipe 102 may be disposed on a plane 105 parallel or substantially parallel to the first pipe 101, the plane being at an angle of ±15° or less from the perfectly parallel direction to the first pipe 101. Furthermore, in the plane 105 parallel or substantially parallel to the first pipe 101, the third pipe 103 disposed on the second pipe 102 may be disposed on a plane being at an angle of ±10° or less from the perfectly parallel direction to the first pipe 101, or may be disposed on a plane being at an angle of ±5° or less from the perfectly parallel direction.

[0024] 3 is a schematic plan view illustrating the connection direction of a third pipe in the piping structure used in the present invention. Fig. 3 is a schematic plan view of a second pipe disposed substantially perpendicular to the first pipe, viewed from above. Fig. 3A shows a first pipe 101 through which a gas containing a cohesive powder flows, a second pipe 102 connected to the first pipe and disposed substantially perpendicular to the first pipe, and a third pipe 103 connected to the second pipe and disposed on the second pipe in a plane 105 substantially parallel to the first pipe. The gas containing a cohesive powder flows in one direction through the first pipe 101, and the second pipe 102 and the third pipe 103 are connected so that the angle (θ1) between the flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe 101 is 0°. 3B similarly shows a case where the second pipe 102 and the third pipe 103 are connected such that the angle (θ1) between the flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe is 20°. FIG. 3C similarly shows a case where the second pipe 102 and the third pipe 103 are connected such that the angle (θ1) between the flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe is 30°. The flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe can each be regarded as a vector. The angle (θ1) between the flow direction 104 of the gas flowing through the first pipe and the flow direction 106 of the purge gas flowing through the third pipe can be calculated in the same manner as the angle between two vectors. The angle (θ1) formed by the flow direction 104 of the gas flowing through the first piping and the flow direction 106 of the purge gas flowing through the third piping is the angle that is 180° or less of the angle formed by the two vectors when the vectors are translated and the starting point of one vector is superimposed on the starting point of the other vector, as shown in the right diagrams of Figures 3(A) to 3(C).FIG. 3D shows a case where the angle (θ1) between the flow direction 104 of the gas flowing through the first pipe and the flow direction 107 of the purge gas flowing through the third pipe 108 corresponding to the comparative example is 150°, which does not fall within the scope of the present invention.

[0025] In addition, in the first pipe through which gas containing a cohesive powder flows in one direction, the flow direction 104 of the gas flowing through the first pipe refers to the main flow direction of the gas and can basically be considered to be parallel to the direction in which the first pipe extends. Since the flow direction 104 of the gas flowing through the first pipe is partially disturbed at the connection with the second pipe, the direction in which the first pipe extends up to the connection between the first pipe and the second pipe can also be used as the reference. The flow direction 106 of the purge gas flowing through the third pipe can also basically be considered to be parallel to the direction in which the third pipe extends up to the connection between the third pipe and the second pipe. Taking these factors into consideration, the third pipe may be disposed in the second pipe.

[0026] By having a specific piping structure connecting the second piping and the third piping such that the angle between the flow direction of the gas flowing through the first piping and the flow direction of the purge gas flowing through the third piping on a plane substantially parallel to the flow direction of the gas flowing through the first piping is within 30°, a downward flow caused by the purge gas hitting the second piping can be efficiently suppressed from flowing into the second piping, as shown in the examples described below. The angle between the flow direction of the gas flowing through the first piping and the flow direction of the purge gas flowing through the third piping on a plane substantially parallel to the flow direction of the gas flowing through the first piping may be within 20°, within 10°, within 5°, or even 0°. The smaller the angle between the flow direction of the gas flowing through the first piping and the flow direction of the purge gas flowing through the third piping on a plane substantially parallel to the flow direction of the gas flowing through the first piping, the more efficiently the purge gas flowing through the third piping can suppress the gas in the first piping from flowing into the second piping.

[0027] The size of the inner diameter (D1) of the first pipe is not particularly limited, and may be, for example, 150.0 mm to 550.0 mm, 152.4 mm to 533.4 mm, or 151.0 mm to 477.8 mm. The first pipe may be a straight pipe without any bends, at least in the range of D1 x 3 (mm) before and after the connection between the first pipe and the second pipe.

[0028] The size of the inner diameter (D2) of the second pipe is not particularly limited, and may be, for example, 45.0 mm to 131.0 mm, 50.8 mm to 130.9 mm, 52.9 mm to 130.8 mm, or 53.0 mm to 127.0 mm. The inner diameter (D2) of the second pipe is typically smaller than the inner diameter (D1) of the first pipe, since the second pipe is prone to clogging due to cohesive powder in the gas flowing through the first pipe. The ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe may be 1 / 12 to 1 / 2, 1 / 10 to 1 / 2.5, or 1 / 9 to 1 / 3.

[0029] The size of the inner diameter (D3) of the third pipe is not particularly limited, and may be, for example, 6.0 mm to 28.0 mm, 6.5 mm to 27.6 mm, or 8.5 mm to 25.4 mm. The inner diameter (D3) of the third pipe may usually be smaller than the inner diameter (D2) of the second pipe, and the ratio (D3 / D2) of the inner diameter (D3) of the third pipe to the inner diameter (D2) of the second pipe may be 1 / 15 to 1 / 2, 1 / 10 to 1 / 2.5, or 1 / 8 to 1 / 3.

[0030] Furthermore, the distance (Dc) from the connection between the first pipe and the second pipe to the connection between the second pipe and the third pipe is represented by the shortest distance from the base of the second pipe to the base of the third pipe, as shown in Fig. 2, and is not particularly limited. For example, the lower limit of Dc may be 50 mm or more in terms of the arrangement of the third pipe, and the upper limit may be 400 mm or less in terms of the clogging suppression effect. The upper limit may be 300 mm or less, or may be 200 mm or less.

[0031] The second pipe may be a straight pipe without any bends from the connection between the first pipe and the second pipe to the connection between the second pipe and the third pipe. The second pipe is not particularly limited, but may be a closed flow path and may be a pipe leading to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

[0032] Furthermore, the third pipe for flowing the purge gas may be a straight pipe without any bends, at least in the range of D3×3 (mm) before the connection between the second pipe and the third pipe.

[0033] In the present invention, the piping structure as described above is installed, and further, a purge gas is supplied to the second pipe through the third pipe at a flow rate predetermined relative to the flow rate of the gas flowing through the first pipe, and the flow rate of the purge gas is controlled so as to suppress the intrusion of cohesive powder in the gas flowing through the first pipe into the second pipe.

[0034] The flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe is not particularly limited, but a standard flow velocity in low-pressure gas design is, for example, 6 m / s to 18 m / s, and may be 8 m / s to 15 m / s.

[0035] The flow velocity (V3) (m / s) of the purge gas flowing through the third pipe may be appropriately set in accordance with the gas flow velocity (V1) through the first pipe so that supplying the purge gas can suppress the intrusion of cohesive powder in the gas flowing through the first pipe into the second pipe. If the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe is excessively large compared to the gas flow velocity (V1) through the first pipe, it may affect instruments connected to the second pipe. Therefore, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe may be designed to be lower than the gas flow velocity (V1) through the first pipe. The ratio (V3 / V1) of the flow velocity (V3) of the purge gas flowing through the third pipe to the gas flow velocity (V1) through the first pipe may be 0.2 to 0.8 and may be appropriately selected. In addition, since the pressure gauge or the like attached at the end of the second pipe is an instrument for detecting the state of the first pipe or the like, it is preferable that the influence of the purge gas from the third pipe on the instrument is small, and therefore the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe is, for example, 1.2 m / s to 14.4 m / s.

[0036] It is preferable that the flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and the inner diameter (D2) (mm) of the second pipe satisfy the following formula (1) in order to efficiently prevent the reaction gas flowing through the first pipe from invading the second pipe: V3 / V1 ≧ 0.01 × D2 − 0.33 (1)

[0037] The relationship between V3 / V1 and D2 (mm) defined in the above formula (1) can be used as an index for controlling the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe. The larger the inner diameter (D2) (mm) of the second pipe, the larger the lower limit value of the velocity ratio (V3 / V1) is. Setting the velocity ratio (V3 / V1) and the inner diameter (D2) (mm) of the second pipe to satisfy the following formula (1) is more effective in suppressing the intrusion of the reaction gas flowing through the first pipe into the second pipe by supplying the purge gas. The relationship between V3 / V1 and D2 (mm) defined in the above formula (1) was derived based on simulation data from examples and comparative examples, as will be described in the examples below. The parameters of a relational expression that holds between D2 (mm) and the lower limit of the velocity ratio (V3 / V1) of the purge gas velocity (V3) to the reactant gas velocity (V1) in the first piping, which is effective for suppressing the intrusion of the reactant gas flowing in the first piping into the second piping by supplying the purge gas, were determined by the least squares method (see FIG. 13 ).

[0038] Furthermore, it is preferable that the flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, the inner diameter (D2) (mm) of the second pipe, and the inner diameter (D1) (mm) of the first pipe satisfy the following formula (2), in order to efficiently prevent the reaction gas flowing through the first pipe from invading the second pipe: V3 / V1 ≧ 2.65 × D2 / D1 − 0.33 (2)

[0039] The relationship between V3 / V1 and D2 / D1 defined in the formula (2) can be used as an index of the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe. The larger the inner diameter ratio (D2 / D1), the larger the lower limit value of the velocity ratio (V3 / V1) is, preferably. Setting the velocity ratio (V3 / V1) and the inner diameter ratio (D2 / D1) to satisfy the following formula (2) is more effective in suppressing the intrusion of the reaction gas flowing through the first pipe into the second pipe by supplying a purge gas. The relationship between V3 / V1 and D2 / D1 defined in the formula (2) was derived based on simulation data from examples and comparative examples, as will be described in the examples below. The parameters of a relational expression that holds between the lower limit of the velocity ratio (V3 / V1) of the purge gas velocity (V3) to the reactant gas velocity (V1) in the first piping and the ratio of the inner diameters (D2 / D1) were determined by the least squares method (see FIG. 14 ), which is effective for suppressing the intrusion of the reactant gas flowing through the first piping into the second piping by supplying the purge gas.

[0040] The purge gas supplied to the second pipe through the third pipe may be appropriately selected depending on the cohesive powder in the gas flowing through the first pipe, and may be, for example, an inert gas or the same type of gas as the gas flowing through the first pipe. Examples of the inert gas include an inert gas or an olefin gas when producing polyolefin, and an inert gas or a propylene gas when producing polypropylene. Examples of the inert gas include nitrogen gas and argon gas, and may be nitrogen gas.

[0041] The purge gas supply means used in the second piping clogging prevention system of the present invention for supplying purge gas toward the second piping through the third piping may be appropriately selected depending on the purge gas used, and includes at least a purge gas supply source.

[0042] Furthermore, the control means for controlling the flow rate of the purge gas used in the clogging suppression system for the second pipe of the present invention may be, for example, a flow-restricting orifice, a flow-regulating valve, etc. Using the control means for controlling the flow rate of the purge gas, the purge gas is controlled to be supplied through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe, so as to suppress the intrusion of cohesive powder in the gas flowing through the first pipe into the second pipe by supplying the purge gas.

[0043] Next, a polyolefin polymerization apparatus including a gas-phase polymerization reactor and a first pipe for transporting a gas containing polyolefin powder removed from the gas-phase polymerization reactor and the piping structure of the present invention, and a method for producing polyolefins using the polyolefin polymerization apparatus will be described.

[0044] The olefin monomer used to produce the polyolefin is not particularly limited, but an α-olefin monomer having from 2 to 20 carbon atoms is preferably used. Specific examples of the α-olefin monomer having from 2 to 20 carbon atoms include ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 1-nonene, 1-octene, 1-heptene, 1-hexene, 1-decene, 1-undecene, and 1-dodecene. In terms of suitability for the application of the present invention, the olefin monomer may be an olefin containing propylene. The polyolefin production method of the present invention may involve homopolymerization of propylene or copolymerization of propylene with an α-olefin monomer other than propylene and having from 2 to 20 carbon atoms.

[0045] In the present invention, gas-phase polymerization refers to a polymerization process in which polymerization is carried out in a gas phase substantially in the absence of a liquid phase. It is sufficient that the phase in which polymerization is carried out is substantially a gas phase, and a liquid may be present within the scope of the present invention. Examples of this liquid include a liquefied monomer-containing liquid for heat removal and an inert hydrocarbon such as hexane used as a solvent when supplying a catalyst. A liquid-phase reaction in which a catalyst diluted in a solvent is supplied and then reacts with a liquefied monomer dissolved in the solvent is also included in the gas-phase polymerization of the present invention.

[0046] Examples of the gas-phase polymerization reactor used in the present invention include a horizontal gas-phase polymerization reactor having an internal agitator that rotates around a horizontal axis, a fluidized bed reactor, etc. Figure 4 is a schematic explanatory diagram showing an example of the arrangement of a polyolefin polymerization apparatus equipped with a horizontal gas-phase polymerization reactor. In Figure 4, the gas-phase polymerization reactor 1 is expressed as a cross-sectional schematic diagram. In Figure 4, the gas-phase polymerization reactor 1 is a hollow vessel having an overall elongated shape consisting of a cylindrical body and hemispherical vessel ends connected to both ends of the body, and is arranged horizontally when the polyolefin polymerization apparatus 50 is installed.

[0047] The internal space of the gas-phase polymerization reactor 1 accommodates an agitator 2 having at least an agitator shaft 2a that rotates in the circumferential direction of the barrel of the gas-phase polymerization reactor 1 and agitator blades 2b fixed on the agitator shaft. The agitator 2 has an agitator shaft 2a that coincides with the central axis of the longitudinal direction of the gas-phase polymerization reactor, and a plurality of agitator blades 2b for stirring attached inside the gas-phase polymerization reactor 1. A motor 3 is disposed on the other end side of the gas-phase polymerization reactor 1 as a drive device for rotating the agitator shaft about its axis.

[0048] Catalyst component supply pipes 4 and 5 are connected to the gas-phase polymerization reactor 1. The catalyst component supply pipes 4 and 5 can be installed at any position as long as they are supplied from the upper part of one end of the horizontal polymerization reactor. Furthermore, the gas-phase polymerization reactor 1 is provided with a plurality of raw material monomer supply ports and a plurality of unreacted gas outlet ports at appropriate intervals at the upper part in the direction of gravity and downstream of the catalyst supply port. Each raw material monomer supply port is connected to a raw material monomer supply pipe 6, and each unreacted gas outlet is connected to an unreacted gas outlet pipe 7. Meanwhile, a plurality of raw material monomer gas supply ports are provided at appropriate intervals at the lower part in the direction of gravity of the gas-phase polymerization reactor 1, in areas facing the raw material monomer supply ports and the unreacted gas outlet. Each raw material monomer gas supply port is connected to a raw material monomer gas supply pipe 10. Furthermore, a polymer outlet is provided at the lower part in the direction of gravity of the gas-phase polymerization reactor 1 near the downstream end of the reaction, and a polymer outlet pipe 11 is connected to it.

[0049] Hereinafter, a method for producing a polyolefin by gas-phase polymerization using the gas-phase polymerization reactor 1 will be described using an example in which at least propylene is used as the olefin monomer, and the configuration of the polyolefin polymerization apparatus 50 in FIG. 4 will also be described.

[0050] The catalyst is introduced into the gas-phase polymerization reactor 1 through catalyst component supply pipes 4 and 5. When the catalyst components are added to the upstream portion of the reactor, they can move to the downstream side of the reactor while growing as polymer particles through polymerization. The catalyst component supply pipe 4 may be a pipe for supplying the main component of the catalyst, such as a solid catalyst component containing a Ziegler-based solid catalyst component or a metallocene complex, as well as other polymerization catalyst components. The catalyst component supply pipe 5 may be a pipe for supplying a cocatalyst, an organoaluminum compound, and other polymerization catalyst components. The catalyst may be supplied to the gas-phase polymerization reactor in powder form as is, or may be supplied after being diluted with an inert solvent such as a liquid saturated hydrocarbon or mineral oil.

[0051] The raw materials, liquefied propylene and liquefied comonomer, are introduced into the gas-phase polymerization reactor 1 through a plurality of raw material monomer supply ports connected to a raw material monomer supply pipe 6. Gaseous raw materials (comonomer, hydrogen, etc.) are introduced into the gas-phase polymerization reactor 1 through a plurality of raw material monomer gas supply ports connected to a raw material monomer gas supply pipe 10. The propylene and comonomer introduced into the gas-phase polymerization reactor 1 are polymerized in the gas phase in contact with the catalyst while being stirred together with the reaction product by a stirrer, and a propylene-based polymer is synthesized as a polyolefin. Hydrogen acts as a molecular weight modifier.

[0052] The polymerization conditions, such as temperature and pressure, of the gas-phase polymerization method are not particularly limited and can be set arbitrarily according to the raw material monomer. When the raw material monomer is propylene, the reaction temperature, polymerization pressure, and residence time in the gas-phase polymerization reactor are as follows. The lower limit of the reaction temperature is preferably 0°C or higher, more preferably 30°C or higher, and particularly preferably 40°C or higher, and the upper limit is preferably 100°C or lower, more preferably 90°C or lower, and particularly preferably 80°C or lower. The lower limit of the polymerization pressure is atmospheric pressure or higher, preferably 600 kPaG or higher, more preferably 1000 kPaG or higher, and particularly preferably 1600 kPaG or higher, and the upper limit is preferably 4200 kPaG or lower, more preferably 3500 kPaG or lower, and particularly preferably 3000 kPaG or lower. The residence time in the gas-phase polymerization reactor is arbitrarily adjusted according to the reactor configuration and product index, but is generally set within the range of 30 minutes to 10 hours. The stirring speed of the stirrer is adjusted arbitrarily according to the reactor configuration, size, product index, etc., but generally, the number of rotations is 10 to 50 min －１ It is set within the range.

[0053] The heat of polymerization generated during polymerization is removed by the heat of vaporization (latent heat of vaporization) of the feed liquefied propylene supplied through a feed monomer supply pipe 6 located at the upper part of the gas-phase polymerization reactor 1 in the direction of gravity. Unreacted propylene gas is discharged to the outside of the reaction system through an unreacted gas withdrawal pipe 7 located at the upper part of the gas-phase polymerization reactor 1 in the direction of gravity, where it is partially condensed in a condenser 12 and separated into a liquid phase and a gas phase in a gas-liquid separation tank 13. The separated liquid phase is reintroduced via the feed monomer supply pipe 6 into multiple feed monomer supply ports located at the upper part of the gas-phase polymerization reactor 1 in the direction of gravity to remove the heat of polymerization. Meanwhile, the separated gas phase is mixed with comonomer gas, hydrogen for molecular weight control, and the like, and is reintroduced via the feed monomer gas supply pipe 10 by the driving force of a compressor 14 into multiple feed monomer gas supply ports located at the lower part of the gas-phase polymerization reactor 1 in the direction of gravity. The feed propylene is supplied to the gas-liquid separation tank 13 via a feed propylene etc. supply pipe 15. Furthermore, other raw materials (comonomers, hydrogen, etc.) are supplied into the reaction system in the form of gases through a gas raw material supply pipe 16, or in the form of liquids through a raw material propylene etc. supply pipe 15. The polymer particles, which are the reaction product, move from the upstream to the downstream within the polymerization reaction chamber while being mixed by stirring, are discharged outside the reaction system through a polymer withdrawal pipe 11, are separated in a gas recovery machine, and are then recovered in a powder recovery machine (not shown).

[0054] Furthermore, the polyolefin polymerization apparatus 50 used in the present invention includes the piping structure of the present invention, and includes a first pipe for transferring a gas containing polyolefin powder taken out from the gas-phase polymerization reactor 1. In the polyolefin polymerization apparatus 50 of Figure 4, the first pipe 101 for transferring a gas containing polyolefin powder taken out from the gas-phase polymerization reactor 1 may be an unreacted gas vent pipe 7. A pipe 8 leading to a pressure gauge (not shown) is further connected to the unreacted gas vent pipe 7, and a pipe 9 for flowing a purge gas is further connected to the pipe 8. In the polyolefin polymerization apparatus 50 of FIG. 4 , a first pipe 101 (unreacted gas withdrawal pipe 7) for transferring a gas containing polyolefin powder removed from the gas-phase polymerization reactor 1 includes a second pipe 102 (pipe 8 leading to a pressure gauge (not shown)) disposed substantially perpendicular to the first pipe 101, and a third pipe 103 (pipe 9 for flowing a purge gas) connected to the second pipe 102 and disposed in the second pipe 102 in a plane substantially parallel to the first pipe 101 (piping structure 200).

[0055] In the polyolefin polymerization apparatus 50 of Figure 4, a gas containing polyolefin powder flows in one direction through the first pipe 101 (7), and the second pipe 102 (8) and the third pipe 103 (9) are connected so that the angle between the flow direction of the gas flowing through the first pipe 101 (7) and the flow direction of the purge gas flowing through the third pipe 103 (9) on a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°, and a purge gas is supplied through the third pipe 103 (9) toward the second pipe 102 (8) at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe 101 (7). As a result, in the polyolefin production method of the present invention, the pipe 8 leading to the pressure gauge is prevented from being blocked by polyolefin powder contained in the gas flowing through the unreacted gas withdrawal pipe 7, making it possible to produce polyolefins stably over a long period of time.

[0056] FIG. 5 is a schematic diagram showing an example of the arrangement of a polyolefin polymerization apparatus equipped with a vertical fluidized bed reactor as a gas-phase polymerization reactor. In FIG. 5, the fluidized bed reactor 21 is depicted as a cross-sectional schematic diagram. In the polyolefin polymerization apparatus 70 of FIG. 5, a catalyst component supply pipe 22 is connected to the fluidized bed reactor 21. A raw material supply pipe 23 is connected to the lower part of the fluidized bed reactor 21 in the direction of gravity. A plurality of raw material supply pipes may be provided depending on the type of raw material. Furthermore, an unreacted gas vent pipe 24 is connected to the upper part of the fluidized bed reactor 21 in the direction of gravity. The unreacted gas passing through the unreacted gas vent pipe 24 is connected to be recycled to the raw material supply pipe 23 via a heat exchanger 27 and a compressor 28. Furthermore, a polymer vent port is provided at the lower part of the gas-phase polymerization reactor 1 in the direction of gravity, to which a polymer vent pipe 29 is connected.

[0057] Furthermore, the polyolefin polymerization apparatus 70 used in the present invention includes a first pipe for transferring a gas containing polyolefin powder removed from the fluidized bed reactor 21, and includes the piping structure of the present invention. In the polyolefin polymerization apparatus 70 of Figure 5, the first pipe 101 for transferring a gas containing polyolefin powder removed from the fluidized bed reactor 21 may be the unreacted gas vent pipe 24. A pipe 25 leading to a thermometer (not shown) is further connected to the unreacted gas vent pipe 24, and a pipe 26 for flowing a purge gas is further connected to the pipe 25. In the polyolefin polymerization apparatus 70 of FIG. 5 , a first pipe 101 (unreacted gas withdrawal pipe 24) for transferring a gas containing polyolefin powder removed from the fluidized bed reactor 21 includes a second pipe 102 (pipe 25 leading to a thermometer (not shown)) disposed substantially perpendicular to the first pipe 101, and a third pipe 103 (pipe 26 for flowing a purge gas) connected to the second pipe 102 and disposed in the second pipe 102 in a plane substantially parallel to the first pipe 101 (piping structure 200).

[0058] In the polyolefin polymerization apparatus 70 of Figure 5, a gas containing polyolefin powder flows in one direction through the first pipe 101 (24), and the second pipe 102 (25) and the third pipe 103 (26) are connected so that the angle between the flow direction of the gas flowing through the first pipe 101 (24) and the flow direction of the purge gas flowing through the third pipe 103 (26) on a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°, and a purge gas is supplied through the third pipe 103 (26) toward the second pipe 102 (25) at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe 101 (24). As a result, in the polyolefin production method of the present invention, the pipe 25 leading to the thermometer is prevented from being clogged by polyolefin powder contained in the gas flowing through the unreacted gas withdrawal pipe 24, making it possible to produce polyolefins stably over a long period of time.

[0059] The size of the gas phase polymerization reactor is optional depending on the type of reaction, etc. The volume is usually 0.1 m ３ From the viewpoint of industrial productivity and economic efficiency, ３ The length to diameter ratio is preferably 2.0 or more from the viewpoint of industrial productivity and economic efficiency.

[0060] The gas-phase polymerization reactors may be arranged in any manner as long as it does not impair the gist of the present invention. The gas-phase polymerization reactors may be one or more, and if multiple reactors are used, they may be connected in series or in parallel. A preferred example is a polymerization reactor in which two to four gas-phase polymerization reactors are connected in series. In particular, when producing a block copolymer of propylene and another α-olefin, an arrangement including at least two reactors connected in series is preferred. There are no particular limitations on the arrangement of two or more reactors. However, in the case of a multi-vessel horizontal polymerization reactor having an agitator that rotates around a horizontal axis, it is preferable to arrange the agitator shaft of the upstream reactor at the same height or higher than the agitator shaft of the downstream reactor, and more preferably at a certain height higher than the agitator shaft of the downstream reactor.

[0061] In addition, the entrainment amount in the polyolefin production method of the present invention means the amount of particles that pass through the unreacted gas extraction pipe installed on the upper vessel wall or the like of the reactor (or the side or bottom) and are discharged out of the reactor together with the unreacted gas relative to the amount of polyolefin such as propylene polymer produced. A specific method for measuring the entrainment amount is, for example, to weigh the amount of fine particles [g / kg] removed by a particulate removal device such as a cyclone or a bag filter installed before the condenser and divide it by the amount of production. When producing polyolefin, the entrainment amount is preferably 0.10 g / kg or less. If this value is high, the increase in entrainment may increase the load and adhesion on the gas exhaust pipe system, or the inflow of fine particles into the condenser may reduce the gas condensation capacity.

[0062] The present invention has been described in detail above using a polyolefin production method as an example, to which the method of the present invention for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe is suitably applied. However, the present invention is not limited to the case where the cohesive powder is polyolefin powder. The method of suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, the system for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe, and the piping structure for suppressing clogging of the second pipe due to cohesive powder in the gas flowing through the first pipe of the present invention can also be applied to other cohesive powders.

[0063] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples alone.

[0064] Example 1 Using a polyolefin polymerization apparatus configured as shown in Figure 4, continuous polymerization was carried out over a long period of time under the following polymerization conditions. (1) Configuration of Polyolefin Polymerization Apparatus As the gas-phase polymerization reactor, a gas-phase polymerization reactor having a length of 16 m and a body inner diameter of 2.9 m, and a horizontal gas-phase polymerization reactor equipped with an agitator having an agitation shaft with an agitation blade attached were used. The rotation speed of the agitation shaft was 16 min －１4 and 1, the polyolefin polymerization apparatus includes an unreacted gas vent pipe (first pipe), and a pipe (second pipe) connected to the first pipe and leading to a pressure gauge disposed substantially perpendicular to the first pipe. The inner diameter (D1) of the first pipe was 248.8 mm, and the inner diameter (D2) of the second pipe was 78.1 mm.

[0065] (2) Configuration and Arrangement of the Third Pipe for Flowing Purge Gas As shown in Figures 4 and 1, the third pipe for flowing purge gas was connected to the second pipe and disposed in a plane substantially parallel to the first pipe. The inner diameter (D3) of the third pipe was 16.7 mm, and the distance (Dc) from the connection between the first pipe and the second pipe to the connection between the second pipe and the third pipe was approximately 200 mm. The second pipe and the third pipe were connected so that the angle (θ1) between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe was 0°. (3) Flow Velocity of Purge Gas in the Third Pipe The flow velocity (V1) (m / s) of the gas containing polyolefin powder flowing through the first pipe was 9.64 m / s. Propylene gas was used as the purge gas. The flow velocity (V3) (m / s) of the purge gas flowing through the third pipe was set to 6.09 m / s, and the purge gas was supplied through the third pipe toward the second pipe. V3 / V1 = 0.63. The flow velocity (V1) (m / s) of the gas containing polyolefin powder flowing through the first pipe, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and the inner diameter (D2) (mm) of the second pipe satisfied the relationship represented by the formula (1). Furthermore, the flow velocity (V1) (m / s) of the gas containing polyolefin powder flowing through the first pipe, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, the inner diameter (D2) (mm) of the second pipe, and the inner diameter (D1) (mm) of the first pipe satisfied the relationship represented by the formula (2).

[0066] (4) Polymerization conditions Polymerization temperature: 60 to 70°C Polymerization pressure: 2.2 to 2.5 MPaG Propylene homo-gas phase polymerization and propylene-ethylene random gas phase polymerization (5) Accumulated operation time Accumulated operation time: about 12 months (6) Results Even when continuous polymerization was carried out for a long period of time, the pressure was not measured using the pressure gauge connected to the second piping, and no blockage of the second piping was observed as a result of an open inspection.

[0067] Comparative Example 1 Continuous polymerization was carried out over a long period of time in the same manner as in Example 1, except that the third pipe for flowing a purge gas was not attached and no purge gas was flowed toward the second pipe. After about two months, the readings of the pressure gauge connected to the second pipe became unstable, and when the second pipe was removed and observed, clogging of the second pipe with polyolefin powder was observed.

[0068] In the following examples and comparative examples, a fluid simulation was performed on the flow of olefin gas (hereinafter sometimes simply referred to as "reaction gas") containing polyolefin powder from the first pipe to the second pipe. The fluid simulation was used to examine the effect of the setting conditions of the purge gas flowing through the third pipe on gas intrusion from the first pipe to the second pipe. A simulation model was created for the fluid simulation using fluid simulation software (manufactured by ANSYS, Inc., product name ANSYS Fluent version 2023R2). The simulation model was divided into hexahedrons or polyhedrons with an interval of approximately 4 mm, and calculations were performed with the gas flow rate set as a boundary condition. The following conditions were applied to the simulation model: the output pressure of the first pipe was 2450 kPaG, the inner diameter (D1) of the first pipe was 248.8 mm, the length of the first pipe was 2000 mm, the length of the second pipe was 616 mm, and the reaction gas in the first pipe was a gas mainly composed of propylene (gas density: 53.5 kg / m ３ , gas viscosity: 0.0978 mPa s). In the simulation in which the third pipe was installed, the following conditions were further applied: the length of the third pipe was 256 mm, the distance between the second and third pipes (Dc) was 166 mm, and the purge gas in the third pipe was a gas mainly composed of propylene (gas density: 53.5 kg / m３ , gas viscosity: 0.0978 mPa·s). The setting conditions changed in each example are specifically shown in each example. A Realizable k-ε model was used as the turbulence model, and simulations were performed by solving the transport equation for the chemical species. In the simulation results, the degree to which the reactant gas from the first pipe flowed into the second pipe was observed as the reactant gas concentration in the second pipe. Note that, even if the same gas containing propylene as the main component was used in the simulation, the reactant gas from the first pipe and the purge gas from the third pipe were distinguished, and the reactant gas concentration in the second pipe below refers to the concentration of the reactant gas flowing in from the first pipe.

[0069] <Comparative Example 2> Similar to Comparative Example 1, a simulation was performed on the flow of the reactant gas in the first pipe when a third pipe for flowing the purge gas was not installed and no purge gas was flowing toward the second pipe. The inner diameter (D2) of the second pipe was 78.1 mm, and the flow velocity (V1) (m / s) of the reactant gas flowing through the first pipe was 9.64 m / s. As a result, as shown schematically in FIG. 6, at the connection point between the first pipe 101 and the second pipe 102, a flow 110 was generated in which the reactant gas from the first pipe penetrated deep into the second pipe 102, resulting in an increase in the reactant gas concentration in the first pipe in the second pipe. This is believed to be the cause of the blockage of the second pipe. As shown schematically in FIG. 6, at the connection point between the first pipe and the second pipe, the reactant gas from the first pipe penetrated along the inner wall 102a of the second pipe on the flow direction 104 side of the first pipe.

[0070] Example 2 Similar to Example 1, a third pipe for flowing purge gas was attached, and a gas flow was simulated when purge gas was supplied toward the second pipe through the third pipe. As shown in FIG. 2 , a third pipe for flowing purge gas was connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe. The inner diameter (D3) of the third pipe was 16.7 mm. The second pipe and the third pipe were connected so that the angle (θ1) between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe was 0°. The inner diameter (D2) of the second pipe was 78.1 mm, and the flow velocity (V1) (m / s) of the reaction gas flowing through the first pipe was 9.64 m / s. The flow velocity (V3) (m / s) of the purge gas flowing through the third pipe was 6.09 m / s. As a result, as shown in FIG. 7 , the purge gas supplied to the second pipe through the third pipe 103 hit the inner wall 102a of the second pipe 102 on the purge gas flow direction 106 side and split into upper and lower flows. A downward flow 120 of the purge gas was generated along the inner wall 102a of the second pipe on the purge gas flow direction side. This downward flow 120 of the purge gas pushed back the flow 110 of the reactant gas from the first pipe that had entered along the inner wall 102a of the second pipe on the flow direction side of the first pipe, thereby suppressing the inflow of the reactant gas from the first pipe. The reactant gas from the first pipe mixed with the downward purge gas formed a downward flow 111, and a portion of this flowed through the second pipe while mixing with the purge gas. However, the reactant gas concentration in the first pipe remained low in the second pipe. This is thought to prevent clogging of the second pipe for a long period of time. In Example 2, the second pipe and the third pipe were connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe on a plane substantially parallel to the flow direction of the gas flowing through the first pipe was 0°, and a downward flow of purge gas was generated on the inner wall side of the second pipe where the reaction gas from the first pipe enters, which is thought to have efficiently suppressed the inflow of gas into the first pipe.

[0071] Comparative Example 3 A simulation of the gas flow when supplying purge gas to the second pipe through the third pipe was performed under the same conditions as in Example 2, except that the third pipe for supplying purge gas was connected to the second pipe so that the angle (θ1) between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe on a plane substantially parallel to the flow direction of the gas flowing through the first pipe was 180°. Hereinafter, the angle at which the second pipe and the third pipe are connected at the angle (θ1) between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe on a plane substantially parallel to the flow direction of the gas flowing through the first pipe may be simply referred to as the "connection angle (θ1)." As a result, as schematically shown in FIG. 8 , the purge gas supplied to the second pipe through the third pipe 108 hits the inner wall 102b of the second pipe on the purge gas flow direction 107 side and splits into upper and lower portions. The inner wall 102b of the second pipe on the purge gas flow direction 107 side was opposite the inner wall 102a of the second pipe on the flow direction side of the first pipe. Therefore, the downward flow 120 of the purge gas had almost no effect of pushing back the flow 110 of the reaction gas from the first pipe that had entered along the inner wall 102a of the second pipe on the flow direction 104 side of the first pipe. The reaction gas 110 from the first pipe that entered along the inner wall 102a of the second pipe mixed with the purge gas to form an upward flow 112 and a downward flow 111, and the reaction gas from the first pipe flowed into the second pipe with a high concentration. When the connection angle (θ1) was set to 180°, the purge gas supplied toward the second pipe through the third pipe promoted the inflow of the reaction gas from the first pipe, reducing the effect of suppressing clogging of the second pipe by the purge gas.

[0072] Based on Examples 1 and 2 and Comparative Examples 1 to 3, it was considered that the arrangement of the third pipe for flowing the purge gas was important in order to suppress the intrusion of the reaction gas flowing through the first pipe into the second pipe by supplying the purge gas. It was also considered that control of the flow rate (V3) of the purge gas in the third pipe was important in order to suppress the intrusion of the reaction gas flowing through the first pipe into the second pipe by supplying the purge gas. Therefore, in the following, a simulation was performed to examine the effect on the gas flow in the first pipe by changing the gas flow rate (V1) in the first pipe, the inner diameter (D2) of the second pipe, the arrangement (connection angle (θ1)) of the third pipe for flowing the purge gas, and the flow rate (V3) of the purge gas in the third pipe.

[0073] Example 3 A simulation was performed to determine the average concentration (vol%) of the reactant gas in the second pipe by changing the reactant gas velocity (V1) and the purge gas velocity (V3) in the first pipe, using the same inner diameter (D2) of 78.1 mm and connection angle (θ1) as in Example 1, as shown in Table 1. Table 1 also shows the results of the average concentration (vol%) of the reactant gas in the second pipe.

[0074]

[0075] FIG. 9 is a graph showing the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions in Table 1. Here, the average reactant gas concentration in the second pipe refers to the average reactant gas concentration throughout the entire second pipe (from the junction between the first and second pipes to the tip of the second pipe). Referring to Table 1 and FIG. 9, it was shown that the reactant gas concentration in the second pipe suddenly increases when the velocity ratio becomes smaller than V3 / V1 = 0.51. The simulation results of the reactant gas concentrations under conditions A, B, and C in FIG. 9 are shown in FIG. 10, respectively. FIG. 10 also shows the average reactant gas concentration at the cross section at the midpoint between the junction between the second and third pipes and the tip of the second pipe, as an evaluation cross section of the second pipe. The average concentration of the reactant gas at the evaluation cross section of the second pipe was a fairly low value of 4.75 vol% under condition A (V3 / V1 = 0.51), 15.2 vol% under condition B (V3 / V1 = 0.46), and 48.7 vol% under condition C (V3 / V1 = 0.41). Under condition A (V3 / V1 = 0.51), the purge gas sufficiently suppressed the intrusion of the reactant gas into the second pipe. However, when V3 / V1 was small, as in condition B or C, the flow rate of V3 was insufficient, resulting in an insufficient suppression effect on the inflow of the reactant gas, and it is believed that the dilution effect of the purge gas was exerted. Therefore, under the same conditions as in Example 1, where the inner diameter (D1) of the first pipe was 248.8 mm and the inner diameter (D2) of the second pipe was 78.1 mm, it was shown that a velocity ratio of V3 / V1 = 0.51 or more was more effective in suppressing the intrusion of the reactant gas into the second pipe by the purge gas. Under these conditions, V3 / V1 = 0.51 was set as the lower limit of the preferable velocity ratio. Note that the asterisks in Figure 9 indicate the predicted average reactant gas concentration values ​​when V1 = 9.64 m / s, V3 = 6.09 m / s, and V3 / V1 = 0.63 in Example 1. In Example 1, clogging of the second pipe was suppressed.

[0076] Example 4 A simulation was performed to determine the average concentration (vol%) of the reactant gas in the second pipe by changing the reactant gas velocity (V1) and the purge gas velocity (V3) in the first pipe, with the inner diameter (D2) of the second pipe set to 65.9 mm and the connection angle (θ1) set to 0°, according to Table 2. Table 2 also shows the results of the average concentration (vol%) of the reactant gas in the second pipe.

[0077]

[0078] FIG. 11 is a graph showing the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the average reactant gas concentration in the second pipe, based on the results of a simulation performed under the conditions in Table 2. Referring to Table 2 and FIG. 11, it was shown that the reactant gas concentration in the second pipe suddenly increased when the velocity ratio became smaller than V3 / V1 = 0.37. The average reactant gas concentration at the evaluation cross section of the second pipe was a fairly low value of 5.44 vol% under condition A (V3 / V1 = 0.37) in FIG. 11, whereas it was 37.9 vol% under condition B (V3 / V1 = 0.30) in FIG. 11. Therefore, it was shown that a velocity ratio of V3 / V1 = 0.37 or greater, under the condition of a first pipe inner diameter (D1) of 248.8 mm and a second pipe inner diameter (D2) of 65.9 mm, is more effective in suppressing the intrusion of the reactant gas into the second pipe by the purge gas. Under these conditions, V3 / V1 = 0.37 was set as the lower limit of the preferable speed ratio.

[0079] Example 5 A simulation was performed to determine the average concentration (vol%) of the reactant gas in the second pipe by changing the reactant gas velocity (V1) and the purge gas velocity (V3) in the first pipe, with the inner diameter (D2) of the second pipe set to 90.2 mm and the connection angle (θ1) set to 0°, according to Table 3. Table 3 also shows the results of the average concentration (vol%) of the reactant gas in the second pipe.

[0080]

[0081] FIG. 12 is a graph showing the purge gas velocity (V3) relative to the reactant gas velocity (V1) in the first pipe and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions in Table 3. Referring to Table 3 and FIG. 12, it was shown that the reactant gas concentration in the second pipe suddenly increased when the velocity ratio became smaller than V3 / V1 = 0.63. The average reactant gas concentration at the evaluation cross section of the second pipe was a fairly low value of 8.21 vol% under condition A (V3 / V1 = 0.63) in FIG. 12, whereas it was 43.7 vol% under condition B (V3 / V1 = 0.57) in FIG. 12. Therefore, it was shown that a velocity ratio of V3 / V1 = 0.63 or greater is more effective in suppressing the intrusion of the reactant gas into the second pipe by the purge gas under the condition of a first pipe inner diameter (D1) of 248.8 mm and a second pipe inner diameter (D2) of 90.2 mm. Under these conditions, V3 / V1 = 0.63 was set as the lower limit of the preferable speed ratio.

[0082] Based on the simulation results shown in Tables 1 to 3, a correlation was found between the lower limit of the velocity ratio (V3 / V1) of the purge gas velocity (V3) to the reactant gas velocity (V1) in the first pipe and the inner diameter (D2) (mm) of the second pipe, which is effective for suppressing the intrusion of the reactant gas flowing through the first pipe into the second pipe by supplying a purge gas, as shown in FIG. 13 . The larger the inner diameter (D2) (mm) of the second pipe, the larger the lower limit of the velocity ratio (V3 / V1). The relationship obtained by the least squares method was V3 / V1 = 0.01 × D2 - 0.33. Therefore, it can be said that setting the velocity ratio (V3 / V1) and the inner diameter (D2) (mm) of the second pipe to satisfy the following formula (1) is effective for suppressing the intrusion of the reactant gas flowing through the first pipe into the second pipe by supplying a purge gas: V3 / V1 ≧ 0.01 × D2 - 0.33 (1)

[0083] Furthermore, based on the simulation results of Tables 1 to 3, a correlation was found between the lower limit of the velocity ratio (V3 / V1) and the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe, which is effective for suppressing the intrusion of the reactant gas flowing through the first pipe into the second pipe by supplying a purge gas, as shown in FIG. 14 . The larger the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe, the larger the lower limit of the velocity ratio (V3 / V1). The relationship obtained by the least squares method was V3 / V1 = 2.65 × D2 / D1 - 0.33. Therefore, it can be said that setting the velocity ratio (V3 / V1) and the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe so as to satisfy the following formula (2) is effective for suppressing the intrusion of the reactant gas flowing through the first pipe into the second pipe by supplying a purge gas. V3 / V1 ≧2.65×D2 / D1-0.33 (2)

[0084] Furthermore, based on the simulation results in Tables 1 to 3, a correlation was found between the allowable upper limit of the average reactant gas concentration in the second pipe and the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe (see Table 4 and FIG. 15).

[0085]

[0086] The larger the ratio (D2 / D1) of the inner diameter (D2) of the second pipe to the inner diameter (D1) of the first pipe, the lower the allowable upper limit of the average reactant gas concentration (C ｒｇ The relationship obtained by the least squares method is C ｒｇ = 53.23 × D2 / D1 - 1.83. Therefore, the allowable upper limit of the average reactant gas concentration (C ｒｇ ) can be set so that D2 / D1 satisfies the following formula (3): ｒｇ ≦53.23×D2 / D1-1.83 (3)

[0087] Example 6 A simulation was performed to determine the average concentration (vol%) of the reactant gas in the second pipe by changing the connection angle (θ1), the reactant gas velocity (V1), and the purge gas velocity (V3) of the first pipe, with the inner diameter (D2) of the second pipe set to 78.1 mm, according to Table 5. Table 5 also shows the results of the average concentration (vol%) of the reactant gas in the second pipe. Note that in the simulation of Example 6, examples in which the connection angle (θ1) exceeds 30° correspond to comparative examples.

[0088]

[0089] 16 is a graph showing the relationship between the connection angle θ1 (°) and the average reactant gas concentration in the second pipe for the results of a simulation performed under the conditions in Table 5. Referring to Table 5 and FIG. 16, it was shown that when the connection angle θ1 (°) is greater than 30°, the reactant gas concentration in the second pipe increases, and the effect of the purge gas in suppressing the intrusion of the reactant gas into the second pipe decreases. Therefore, it was shown that setting the connection angle θ1 (°) in the range of 0° to 30° is an effective arrangement for suppressing the intrusion of the reactant gas into the second pipe by the purge gas.

[0090] A simulation was performed in the same manner as in Example 3, except that Dc was changed from 166 mm to 83 mm or 332 mm under the conditions of Example 3, and the same results as in Example 3 were obtained. Furthermore, a simulation was performed in the same manner as in Example 3, except that the purge gas in the third pipe was changed to nitrogen gas under the conditions of Example 3, and the same results as in Example 3 were obtained.

[0091] REFERENCE SIGNS LIST 1 Gas phase polymerization reactor 2 Agitator 2a Agitator shaft 2b Agitator blade 3 Motor 4 Catalyst component supply pipe 5 Catalyst component supply pipe 6 Raw material monomer supply pipe 7 Unreacted gas withdrawal pipe 8 Pipe 9 Pipe 10 Raw material monomer gas supply pipe 11 Polymer withdrawal pipe 12 Condenser 13 Gas-liquid separation tank 14 Compressor 15 Raw material propylene etc. supply pipe 16 Gaseous raw material supply pipe 21 Fluidized bed reactor 22 Catalyst component supply pipe 23 Raw material supply pipe 24 Unreacted gas withdrawal pipe 25 Pipe 26 Pipe 27 Heat exchanger 28 Compressor 29 Polymer withdrawal pipe 50 Polyolefin polymerization apparatus 70 Polyolefin polymerization apparatus 101 First pipe 102 Second pipe 102a Inner wall of second pipe on the flow direction side of first pipe 102b Inner wall of second pipe 103 Third pipe 104 Flow direction of gas flowing through first pipe 105 Plane substantially parallel to the first pipe 106 Flow direction of purge gas flowing through third pipe 107 Flow direction of purge gas flowing through third pipe (Comparative example) 108 Third pipe (Comparative example) 110 Flow of reaction gas in first pipe entering second pipe 111 Downward flow of reaction gas in first pipe 112 Upward flow of reaction gas in first pipe 120 Downward flow of purge gas 200 Piping structure

Claims

1. A method for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the gas containing the cohesive powder flows in one direction through the first pipe; the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; and supplying the purge gas through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing through the first pipe.

2. The method for suppressing clogging of a second pipe according to claim 1, wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

3. The method for suppressing clogging of the second pipe according to claim 1 or 2, wherein a flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe, a flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and an inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 − 0.33 (1) 4. A method for suppressing clogging of a second pipe according to any one of claims 1 to 3, wherein the cohesive powder is polyolefin powder.

5. A system for suppressing clogging of a second pipe due to cohesive powder in a gas flowing through a first pipe, comprising: a first pipe for flowing a gas containing a cohesive powder; a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, wherein the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing through the first pipe and the flow direction of the purge gas flowing through the third pipe in a plane substantially parallel to the flow direction of the gas flowing through the first pipe is within 30°; purge gas supply means for supplying purge gas toward the second pipe through the third pipe; and control means for controlling the flow rate of the purge gas so as to suppress intrusion of the cohesive powder in the gas flowing through the first pipe into the second pipe by supplying the purge gas.

6. The second pipe clogging suppression system according to claim 5, wherein the second pipe is in communication with at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

7. The system for suppressing clogging of a second pipe according to claim 5 or 6, wherein the control means controls the flow rate of the purge gas so that the flow velocity (V1) (m / s) of the gas containing the cohesive powder flowing through the first pipe, the flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and the inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 − 0.33 (1) 8. A second pipe clogging prevention system according to any one of claims 5 to 7, wherein the cohesive powder is polyolefin powder.

9. A piping structure for suppressing clogging of the second piping by cohesive powder in the gas flowing through the first piping, comprising: a first piping for flowing gas containing a cohesive powder; a second piping connected to the first piping and arranged substantially perpendicular to the first piping; and a third piping connected to the second piping and arranged on the second piping in a plane substantially parallel to the first piping, for flowing purge gas, wherein the second piping and the third piping are connected so that the angle between the flow direction of the gas flowing through the first piping and the flow direction of the purge gas flowing through the third piping in a plane substantially parallel to the flow direction of the gas flowing through the first piping is within 30°.

10. A piping structure for suppressing clogging of a second pipe as described in claim 9, wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

11. A piping structure for suppressing clogging of the second pipe as described in claim 9 or 10, wherein the cohesive powder is polyolefin powder.

12. A method for producing polyolefins using a polyolefin polymerization apparatus comprising a gas phase polymerization reactor and a first pipe for transporting a gas containing polyolefin powder removed from the gas phase polymerization reactor, wherein the polyolefin polymerization apparatus comprises: a second pipe connected to the first pipe and disposed substantially perpendicular to the first pipe; and a third pipe connected to the second pipe and disposed in the second pipe in a plane substantially parallel to the first pipe for flowing a purge gas, the gas containing polyolefin powder flowing in one direction in the first pipe; the second pipe and the third pipe are connected so that the angle between the flow direction of the gas flowing in the first pipe and the flow direction of the purge gas flowing in the third pipe in a plane substantially parallel to the flow direction of the gas flowing in the first pipe is within 30°; and the method for producing polyolefins comprises supplying a purge gas through the third pipe toward the second pipe at a predetermined flow rate relative to the flow rate of the gas flowing in the first pipe.

13. The method for producing polyolefins according to claim 12, wherein the second pipe is connected to at least one of a pressure gauge, a safety valve, a thermometer, a release valve, and a differential pressure gauge.

14. The method for producing a polyolefin according to claim 12 or 13, wherein a flow velocity (V1) (m / s) of the gas containing polyolefin powder flowing through the first pipe, a flow velocity (V3) (m / s) of the purge gas flowing through the third pipe, and an inner diameter (D2) (mm) of the second pipe satisfy the following formula (1): V3 / V1 ≧ 0.01 × D2 − 0.33 (1)

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