JP2703812B2 - Gas dispersion plate of fluidized bed type gas phase polymerization equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fluidized bed type gas phase polymerization apparatus, and more particularly to a gas dispersion plate suitable for fluidized bed type gas phase polymerization of olefins.

[Prior art] In the field of polymerization of olefins using a highly active catalyst, a gas phase polymerization method in which a catalyst removal operation after polymerization and a low molecular weight polymer removal operation can be omitted, particularly a gas phase polymerization method using a fluidized bed polymerization apparatus, has recently been used. , Widely used.

FIG. 4 shows a typical example of a case where a polymerization reaction of olefins is carried out by a fluidized bed reactor. A gas dispersion plate 4 for uniformly supplying an olefin gas or a gas containing olefin to the fluidized bed section 9 is attached to the reactor 3. The gas introduced from the gas suction part 5 at the lower part of the reactor is uniformly dispersed by the gas dispersion plate 4 and rises to fluidize the polymer particles in the fluidized bed part 9, where the polymerization reaction proceeds. The unreacted gas that has risen from the fluidized bed section 9 is taken out from the gas discharge section 6 in the upper part of the reactor, cooled, sent to the gas suction section 5 again, and used for circulation.

If the gas is not uniformly dispersed by the gas dispersion plate 4,
Stirring and mixing of the fluidized bed portion 9 become uneven, and in the fluidized bed portion, particularly in the corner portion 10 of the fluidized bed formed by the side wall of the reactor and the gas dispersion plate 4, the removal of polymerization heat becomes insufficient, and Troubles such as lumps and adhesion of the polymer to the inner surface of the reactor occur, and there is a high risk of stopping operation and deteriorating product quality.

As the structure of the gas dispersion plate, other than the conventionally known perforated plate,
In order to solve the above problems, there have been proposed ones in which various caps are mounted on a perforated plate. For example, JP-A-58-1547
JP-A-58-196205 discloses a triangular pyramid cap, JP-A-58-196205 discloses a cap using a partition wall, JP-A-58-201802 discloses a bubble cap, and JP-A-61-106608 discloses an angle cap. Suggested or exemplified.

[Problems to be solved by the invention]

If a gas dispersion plate having a small pore size is used, the flow rate of gas passing through the pores is greatly reduced due to slight adhesion of polymer particles, and clogging is likely to occur. Further, when the unreacted gas containing the polymer fine powder taken out from the gas discharge unit 6 at the upper part of the reactor is circulated and used, the polymer fine powder cannot pass through the gas dispersion plate and clog the gas dispersion plate from below. There is. If clogging of the gas dispersion plate occurs, long-term operation of the polymerization apparatus cannot be continued.

When a gas dispersion plate having a large pore diameter is used, the above-described problem of clogging can be solved to some extent, but two other problems described below occur.

The first problem is that the polymer particles fall to the lower part of the gas dispersion plate, and adhere to the wall or clump at the lower part of the gas dispersion plate.

The second problem is that the distance between the holes, that is, the pitch becomes longer, and a portion having poor flow occurs between the holes. In order to prevent clogging and falling to the lower part of the gas dispersion plate, it is necessary to keep the gas flow rate per hole at a certain level or more. In this case, when the gas flow rate per hole is increased, the total number of holes in the gas dispersion plate is reduced, and as a result, the pitch is increased. With a simple perforated plate that blows gas vertically upward when the pitch is long, polymer particles in the middle of the holes just above the gas dispersion plate cannot be blown off by the gas, and the polymer gas Adhesion to the dispersion plate and lumps occur.

As described in the section of the prior art, many proposals have been made to solve the above two problems by providing caps on the respective holes. However, in these methods, the caps are placed directly above the gas dispersion plate. And the troubles such as adhesion and lumps are likely to occur.

Irrespective of the size of the pore diameter, the corner of the fluidized bed formed by the reactor side wall and the gas dispersion plate is a place where friction against the flow is large, and the flow tends to be poor. In order to prevent the occurrence of the same trouble as described above, it is necessary to maintain a good flow at the location.

The differential pressure generated in the gas dispersion plate of a fluidized bed type gas phase polymerization apparatus generally used is 200 to 10,000 mmAg, and the diameter of the polymerization apparatus is usually 1 to 5 m. In the case of the above differential pressure and diameter, the thickness of the gas dispersion plate needs to be about several mm to 50 mm in order to maintain a sufficient strength with a single gas dispersion plate.

If the gas dispersion plate is subdivided and reinforced with rib supports, etc., the gas dispersion plate with a small thickness will have sufficient strength, but the rib supports will not adhere to polymer particles that become flow obstructions. It is easy to get into troubles such as lumps and lumps.

The problem to be solved by the present invention is to provide a gas dispersion plate for preventing troubles such as adhesion of polymer particles and generation of lumps as described above, and for maintaining good flow.

[Means for solving the problem]

The gas dispersion plate according to the present invention solves the above-mentioned problems, and is as follows.

By making a hole in the gas dispersion plate into which a piece with a slanted hole can be fitted without any gap in the cylindrical or conical trapezoidal plate shown in FIG. 1 and fitting the piece into the hole,
A gas dispersion plate having a large number of oblique gas passages formed on a flat plate.

It is very difficult to make an oblique hole in a wide flat plate, but it is easy to make a small piece. By the above method,
At first glance, a gas dispersion plate in which a large number of oblique flow paths are opened in a wide flat plate can be obtained.

As the size of the gas flow path, the equivalent diameter is required to be 5 times or more the average diameter of the polymer particles. If the diameter is less than 5 times, clogging of the upper surface and the lower portion of the gas dispersion plate tends to occur. In addition, when the cross-sectional shape of the gas flow path is a shape having no angular portion, clogging is less likely to occur.

If the angle θ between the horizontal direction and the flow path shown in FIG. 1 is smaller than a certain angle, the polymer particles do not fall to the lower part of the gas dispersion plate even when the hole diameter is large and the gas flow rate is small. Excessive θ
10-40 is appropriate.

The gas that has passed through the oblique hole flow path is blown obliquely upward from the dispersion plate and forms a flow that crawls on the surface of the dispersion plate. Since the polymer particles have a high ability to blow off the polymer particles and have a wide blow-out range, even if the pitch of the holes is long, the polymer does not adhere or agglomerate in the intermediate portion between the holes directly above the dispersion plate. In order to greatly exhibit this effect, the angle θ is preferably 10 to 40 °, particularly preferably 10 to 20 °.

If the piece and the gas dispersion plate are made the same thickness and manufactured so that there is no step, the finished gas dispersion plate will look like a diagonal hole in the flat plate, and both the upper and lower surfaces of the dispersion plate , Resulting in a flat gas distribution plate. This can prevent troubles such as adhesion and lumps caused by obstruction of flow just above the dispersion plate, which occur when a cap is provided on each hole.

Since the pieces can be mounted in any orientation, the gas blowing direction can be changed in various ways at each point of the distribution plate.

It is particularly desirable to mount the pieces in a direction that produces a swirling flow over the gas distribution plate as the overall gas flow over the gas distribution plate. By generating the swirling flow, the flow of the entire fluidized bed becomes uniform. Even if some lumps are generated, the lumps can be quickly moved and swirled to the outer peripheral portion by centrifugal force, and can be discharged out of the system from the discharge pipe before the lumps grow large.

As for the local gas flow on the gas dispersion plate, the gas discharged from the upstream hole blows out between the holes, and if the polymer particles do not stay in this portion, adhesion and lumps may occur. Trouble can be prevented.

In the corner portion of the fluidized bed formed by the reactor side wall and the gas dispersion plate, poor flow tends to occur, but the gas blowing direction of the piece near the reactor side wall is directed outward, that is, in the direction toward the side wall of the polymerization reactor. By approaching the corners, the flow at the corners becomes good, and troubles such as adhesion and lumps can be prevented.

Further, if the surfaces of the pieces and the gas dispersion plate are smoothed by buffing, electrolytic polishing, or the like, it is effective to prevent troubles such as clogging and adhesion.

When the gas dispersion plate of the large-scale polymerization apparatus is integrated, the plate thickness is about several tens of mm. However, when the angle θ is kept constant and the thickness of the piece is increased, the diameter of the piece increases as shown in FIG. I have to be. As a result, the pitch between the holes is widened, and the polymer particles tend to stay in the middle portion between the holes.

When the thickness of the gas dispersion plate is large, the pitch can be reduced by adopting a structure in which pieces are stacked as shown in FIG. 2D, and the above problem can be solved.

In addition, when a dispersion plate having a large plate thickness is used, sufficient strength can be maintained even when the diameter is large, so that there is no need to divide support even in a large-scale polymerization apparatus, and ribs that are liable to cause poor flow are provided. -There is an advantage that support and the like can be omitted.

As described above, the gas dispersion plate of the present invention is devised with respect to the shape and mounting method of the gas blowing holes, clogging of the holes, falling of polymer particles to the lower portion of the gas dispersion plate, reactor side of the polymer and gas dispersion. It is intended to prevent adhesion to the plate and generation of lumps.

[Action]

When particles pass through the pores, clogging usually occurs unless the pore diameter is a certain multiple of the particle diameter or more. The same concept is applied to the clogging that occurs in the gas dispersion plate, and the dispersion plate of the present invention also needs to have a certain multiple of the average diameter of the polymer particles as the equivalent diameter of the gas flow path. Further, due to the surface finish of the piece and the dispersion plate, particles are less likely to adhere.

In the gas dispersion plate of the present invention, since the angle θ between the oblique gas flow path and the horizontal direction is small, the polymer particles hinder the particles from falling in the lower direction of the gas dispersion plate, and do not fall.

The gas blown to the upper surface of the dispersion plate after passing through the oblique gas passage flows crawling just above the dispersion plate due to the small angle θ. This action completely blows off polymer particles directly above the dispersion plate, especially at locations where the polymer is likely to stay in the middle of the holes, so that the polymer adheres and clumps directly above the dispersion plate. And other troubles can be prevented.

In the gas dispersion plate in which the thickness of the piece and the gas dispersion plate is made the same to prevent a step, the polymer particles are prevented from staying in the concave portions on the upper surface and the lower surface of the dispersion plate. This prevents surface irregularities from being a resistance to the smooth flow of the polymer particles. Further, the surface finish of the pieces and the dispersion plate can reduce the resistance to the flow of the polymer particles.

By changing the mounting direction of the pieces and spraying gas to a place where poor flow is likely to occur, such as an intermediate part between holes or a corner part formed by a reactor side wall and a gas dispersion plate, a polymer at the place is provided. Particles can be blown off, and troubles such as adhesion and clumping can be avoided.

By attaching the pieces in the direction in which the swirling flow is generated on the gas dispersion plate, a good flow can be expressed as the entire fluidized bed. In addition, when a lump of the polymer is generated, the lump moves immediately above the dispersion plate to the outer peripheral direction due to the centrifugal force of the swirling flow of the gas, and reaches the side wall of the reactor. Turn along. By extracting the lump that has reached the side wall of the reactor from a discharge pipe provided on the side wall, the lump stays in the polymerization vessel,
Troubles such as stoppage of operation and deterioration of product quality can be prevented.

〔Example〕

Table 1 shows examples of the present invention in the polymerization of propylene using a fluidized bed type gas phase polymerization apparatus having an inner diameter of 480φ and 1200φ.

In Examples 1 to 6, the gas blowing direction is the direction in which the swirling flow is generated, the outermost circumference, and the gas blowing direction of the piece in the inner row is shifted toward the side wall (the line radially from the center of the reactor to the outer circumference and the gas flow direction). Angle of the blowing direction (φ in Fig. 3) is 105-150
Degree). In Examples 1 to 6, there was no problem such as generation of lumps.

In Examples 7 and 8, the angle φ was set to 90 degrees, and lumps were generated at the corners formed by the side walls of the reactor and the gas dispersion plate.

In Examples 9 and 10, the swirling flow was not used, and the gas blowing directions of all pieces were fixed. Large lumps were generated at the corners where gas did not hit.

In Example 11, since the equivalent diameter of the flow path was small, clogging of the gas dispersion plate occurred immediately after the start of the reaction, and the operation was stopped.

Examples 12 to 17 are examples where the thickness of the gas dispersion plate is large.
Examples 12 and 13 are shown in FIG. 2B, Examples 14 and 15 are shown in FIG.
Is a piece in which a piece is fitted as shown in FIG.

Examples 16 and 17 were fine. In Examples 12 and 13, the polymer particles adhered to the lower part of the piece and clogging occurred. Example 1
As for 4,15, the lump formed on the upper part of the piece immediately after the start of operation, and the operation was stopped.

[Effect] By using the gas dispersion plate according to the present invention, good fluidity can be obtained in a fluidized-bed gas-phase polymerization apparatus, and problems such as polymer adhesion and lumps can be prevented.

[Brief description of the drawings]

FIG. 1 shows a cylindrical shape (FIG. 1A) and a conical trapezoidal shape (FIG. 1A).
FIG. 1 (c) shows a front view and a side view of a cylindrical piece, in which the piece of (b)) is fitted into one hole of the gas dispersion plate. 2A and 2B show an example in which the thickness of the gas dispersion plate is large. FIG. 2A shows an example in which the piece becomes large and the hole pitch becomes wide, and FIGS. (D) shows an example in which the attachment and the pitch are prevented from being widened, and (d) shows an example in which the pieces are stacked in three stages to prevent the pitch from being spread and to eliminate irregularities. FIG. 3 is a plan view of a gas dispersion plate that generates a swirling flow, and FIG. 4 shows a typical example in a case where a polymerization reaction is performed by a fluidized bed. DESCRIPTION OF SYMBOLS 1 ... piece, 2 ... gas dispersion plate 3 ... reactor, 4 ... gas dispersion plate 5 ... gas suction part, 6 ... gas discharge part 7 ... catalyst or polymer introduction pipe 8 ... discharge pipe, 9: Fluidized bed section 10: Corner formed by reactor side wall and gas dispersion plate

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hirozo Ijiri 2 Nakanoshima, Oita City, Oita Prefecture Showa Denko KK Oita Plant (56) References JP-A-58-196205 (JP, A) JP-A 58-154702 (JP, A) JP-A-58-145702 (JP, A)

Claims (7)

(57) [Claims] 1. A gas dispersion plate for a fluidized-bed gas-phase polymerization apparatus having a structure in which a cylindrical or conical trapezoidal piece 1 having an oblique hole is inserted into a large number of holes of a flat plate 2. 2. A gas dispersion plate for a fluidized-bed gas-phase polymerization apparatus having a structure in which a plurality of pieces are stacked to form a flow channel and fitted into a large number of holes of a flat plate. 3. The gas dispersion plate according to claim 1, wherein the piece and the flat plate 2 have the same thickness so that no step is formed. 4. By changing the mounting direction of the piece,
3. The gas dispersion plate according to claim 1, wherein the gas blowing direction can be freely changed. 5. The gas dispersion plate according to claim 1, wherein the pieces are arranged in a direction in which a swirling flow is generated on the gas dispersion plate. 6. A piece is mounted in such a direction as to blow gas to a corner portion of a fluidized bed formed by a side wall of a polymerization apparatus and a gas dispersion plate to improve the flow in the portion. The gas dispersion plate according to (2). 7. The gas dispersion plate is made thicker so that the gas dispersion plate is integrated without being divided, and ribs and supports which are necessary for divided support and are liable to cause poor flow are eliminated.
The gas dispersion plate according to claim 1 or 2.