Fluid distribution in a fluidized bed reactor

A fluid distribution cap (301) for a fluidized bed reactor, comprising a tunnel shaped structure having two opposing walls for attaching to a fluid distribution plate (103), and at least one opening at an end of the tunnel shaped structure. The tunnel shaped structure has an inner surface (302) and an outer surface (303), wherein the inner surface (302) has a curved cross section, and wherein the outer surface (303) has a substantially V-shaped cross section. A fluid distribution plate (103) for a fluidized bed reactor, comprising a plate having a plurality of fluid vent holes (113), a plurality of fluid distribution caps (301), wherein for each fluid vent hole (113) a fluid distribution cap (301) is mounted over said hole (113). At least two mutually neighboring fluid distribution caps (301) are positioned with an opening of a first of the two neighboring fluid distribution caps facing a side of the second of the two neighboring fluid distribution caps. A fluidized bed reactor having a fluid distribution plate (103) and a fluid distribution cap (301).

FIELD OF THE INVENTION

The invention relates to a fluid distribution cap and a fluid distribution plate for a fluidized bed reactor and a fluidized bed reactor comprising the fluid distribution cap and the fluid distribution plate.

BACKGROUND

Fluidized bed reactors are used in polymerization processes involving reactants and/or catalysts in liquid, gas and solid phases. By blowing a fluid or gas reactant into solid particles from below the particles, a fluidized bed is created which floats on the upwards flowing fluid against gravity. When the fluid flow is ceased, the solid particles will come to a rest at the bottom of the fluidized reactor vessel. In order to avoid inlet pluggage or clogging of the reactor vessel, a fluid distribution plate is introduced which allows the fluid to disperse and pass through towards an upper part of the reactor vessel to create the fluidized bed, but which captures the solid particles with fluid distribution caps when the fluidized bed is settled with the reactor shut off and prevents them from contaminating and clogging the reactor inlet.

The fluid distribution plate has fluid vent holes to allow the fluid to pass through to the upper part of the reactor vessel and evenly distribute the fluid across the fluidized bed. The fluid vent holes are covered by a fluid distribution cap to contain the solid particles above the fluid distribution plate, which avoid reactor inlet pluggage which would require a shutdown to remove the clog.

The fluid vent holes and fluid distribution caps cause a pressure drop over the fluid distribution plate, which pressure drop is preferably as low as possible while maintaining even distribution across and above the plate. The reactor and thus the fluid distribution plate should be designed to permit operation for long periods of time without having to shut down for cleaning.

A problem that may occur in known fluidized bed reactors is the flow resistance and stagnant zones of the fluid vent holes in combination with the fluid distribution caps. The design of the fluid vent holes and fluid distribution caps should provide adequate movement of solids between the holes in the distribution plate to prevent sintering of resin in this area, however in stagnant zones underneath or in the vicinity of the distribution caps resins or solids that are entrained in the recycle fluid may be captured by the distribution cap openings which would accumulate and eventually plug the fluid vent holes, requiring undesired maintenance of the fluid bed reactor.

SUMMARY

It is therefore an object of the invention to provide improved fluidization dynamics above the fluid distribution plate whilst avoiding stagnant zones within the distribution caps and above the fluid distribution plate, preventing clogging and plugging of distributor plate vent holes or cap openings, and rendering a fluidized bed reactor mechanically and geometrically simple minimizing maintenance and construction costs.

The object is achieved in a fluid distribution cap for a fluidized bed reactor or a fluidized bed reactor used in a polymerization, comprising a tunnel shaped structure having two opposing walls for attaching to a fluid distribution plate, and at least one opening at an end of the tunnel shaped structure. The tunnel shaped structure has an inner surface and an outer surface, wherein the inner surface has a curved cross section, and wherein the outer surface has a substantially V-shaped cross section.

When mounted on a fluid distribution plate, more specifically over a fluid vent hole in the fluid distribution plate, the curved inner surface cross section incurs less cap resistance thus allowing improved flow of fluid distributed from the fluid distribution cap for a given pressure drop. The rounded curved inner surface causes an even distribution of the fluid flowing through the cap, which substantially reduces stagnant zones within the fluid distribution cap thereby preventing the fluid carrying fines from clogging.

The V-shaped cross section of the outer surface allows a fluid flow parallel to the fluid distribution plate to encounter a side of a neighboring fluid distribution cap to be deflected in a vertical direction, away from the fluid distribution plate towards the fluidized bed. Thus fluidization dynamics of the fluidized bed reactor are improved. With the fluid bed reactor at rest, the fluid distribution cap prevents particles of the settled bed to spill through the fluid vent hole.

In an embodiment, the inner surface has a substantially semicircular cross section. The inner surface can for example be manufactured from a pipe segment.

In an embodiment, the tunnel shaped structure has two openings at opposing ends of the structure. The tunnel shape allows openings at both ends or allow an opening to be closed forcing the fluid flow through the single opening, depending on specific requirements for the fluidized process in the reactor.

In an embodiment, the tunnel shaped structure is a one-piece object. This allows manufacture of the fluid distribution cap from solid material by for example injection molding or casting.

In another embodiment, the structure comprises an angle profile forming the V-shaped outer surface and a pipe segment forming the curved inner surface, the pipe segment attached to an inner part of the angle profile. This allows manufacture of the fluid distribution cap from readily available materials such as the angle profile and the pipe segment.

In an embodiment, the fluid distribution cap has a filler between the angle profile and the pipe segment for closing a clearance between the angle profile and the pipe segment. This prevents stagnant zones between the pipe segment and the angle profile, thus preventing clogging and plugging between these parts. Alternatively, the clearance between the angle profile and the pipe segment may be covered by a cover.

The object is further achieved in a fluid distribution plate for a fluidized bed reactor, comprising a plate having a plurality of fluid vent holes, a plurality of fluid distribution caps as described. For each fluid vent hole a fluid distribution cap is mounted over said hole. The fluid distribution cap is preferably positioned on the fluid distribution plate relative to the vent hole, having the vent hole at its center. The at least two mutually neighboring fluid distribution caps are positioned with an opening of a first of the two neighboring fluid distribution caps facing a side of the second of the two neighboring fluid distribution caps.

The positioning of the two mutually neighboring fluid distribution caps allows a fluid flow from the at least one opening of one fluid distribution cap towards a side of the neighboring fluid distribution cap. The V-shaped cross section of the outer surface causes vertical deflection of the fluid flow. Thus fluidization dynamics of the fluidized bed are improved.

The object is also achieved in a fluidized bed reactor or fluidized bed reactor used in a polymerization process having a fluid distribution plate as described. The upward flow towards the fluidized bed from the fluid distribution plate having the fluid distribution caps as described, improves fluidization dynamics of the fluidized bed reactor. Finally, the invention also concerns the use of a fluid distribution cap according to the invention or fluid distribution plate according to the invention in a polymerization process.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1shows a schematic diagram of an exemplary system100with a fluidized bed reactor101which can be used in a process for polymerization according to the state of the art. The fluid fluidized bed reactor101has a fluidized bed102wherein the process of polymerization is performed. The fluidized bed reactor101can have a product outlet108from where the polymer can be extracted from the system100. Reactants and/or inerts for use in the fluidized bed reactor can be supplied via fluid supply112to the system100. Via fluid inlet106, the fluid enters the fluidized bed reactor101. In an upward flow indicated by the upward pointing arrows through vent holes113in the fluidized bed reactor the fluid passes from a lower end of the fluidized bed reactor101to an upper part having the fluidized bed102. Fluid distribution caps104prevent fluidized bed material from passing through the fluid distribution plate103when the fluidized bed reactor is in rest. Further reactants may be added to the fluidized bed reactor101via supplementary inlet107. Fluid escaping from fluidized bed102is captured in fluid outlet105, and via fluid return111returned to the fluid inlet106of the system100. The fluid in the system is compressed and circulated through the system using a cycle gas compressor110. In heat exchange109any surplus heat can be exchanged with the environment.

FIG. 2ashows an example of a fluid distribution cap in the shape of a pipe segment201aaccording to the state of the art. The fluid distribution cap201ais attached to a fluid distribution plate103at the edges of the pipe segment sidewalls204a. The pipe segment shaped fluid distribution cap201ais placed over vent hole113allowing a fluid outflow202from underneath the pipe segment201a.

Horizontal components205of the fluid outflow202from another fluid distribution cap204acauses a scattered upward flow of the fluid, i.e. flow in various upward directions due to the curved outer surface of the distribution cap201a. Due to the relative steep angle of the side walls201aof the pipe segment shaped fluid distribution cap201a, the outside edges203aof the fluid distribution cap201amay form a stagnant zone where fluid flow is low. In such a stagnant zone, the fluid may clog, thereby contaminating the fluid distribution plate103.

FIG. 2bshows a fluid distribution cap having an angle profile shape201baccording to the state of the art. The fluid distribution cap side walls204bare flat and are connected at a substantially rectangular shaped apex. Fluid outflow207is performed from the fluid vent hole113in a similar way as the pipe segment shaped fluid distribution cap ofFIG. 2a. However the inner curved surface of the pipe segment shaped fluid distribution cap201aallows a better outflow202. The angle profile shaped fluid distribution cap201bmay have stagnant zones near the edges at the inside of the angle profile shaped fluid distribution cap side walls203b. The stagnant zone may cause clogging of the fluid carrying fines passing through the vent hole113and eventually cause plugging.

The angle profile shaped fluid distribution cap201bhas improved deflection of a horizontal component208of the outflow of neighboring fluid distribution caps201bcaused by the flat fluid distribution cap side wall204bwhich is placed substantially at an angle of 45 degrees with respect to the fluid distribution plate103. The deflected fluid flow209is substantially upward as shown inFIG. 2b.

FIG. 3ashows a tunnel shaped fluid distribution cap301having an inner surface with a curved cross section and an outer surface with a V-shaped cross section. The tunnel shaped fluid distribution cap301can be made from a combination of a pipe segment shaped inner element302as inFIG. 2aand an angled profile shaped outer element303as inFIG. 2b. The tunnel shaped fluid distribution cap301is placed over a vent hole113allowing fluid outflow202at both ends of the tunnel shaped pipe segment302. The curved inner surface of the pipe segment shaped inner element302allows efficient outflow202of the fluid, while the V-shaped outer surface, i.e. flat sides305a,305b(which is referred to inFIG. 2bas204b) of the angled profile outer element303allow the efficient upward deflection209of fluid outflows306from neighboring fluid distribution caps301, as shown inFIG. 3band similar to outflows205or202described inFIG. 2a.

Also shown inFIG. 3b, a clearance between the angle profile shaped outer element303and pipe segment shaped inner element302can be filled with a filler304. Alternatively, the clearance304can be covered with an appropriate cover such that the clearance between the pipe segment302and the angle profile303is sealed off from the fluid flow across the distribution plate1203, thereby preventing clogging and plugging of the clearance.

The pipe segment shaped inner element302and the angle profile shaped outer element303can be made from metal and be welded together to the fluid distribution plate103. It can also be contemplated to manufacture the tunnel shaped distribution cap in a one-piece fashion, for example by casting metal in a mold or by injection molding. Other heat resistant materials may also apply. Likewise, filler materials may comprise metal, e.g. carbon steel.

The pipe segment shape of the inner elements302ofFIGS. 3aand 3bcan be semi-circular with a central axis in the plane of the distribution plate103or even underneath the plane of the distribution plate103. Alternative configurations are contemplated inFIGS. 4aand 4b, wherein the central axis of the pipe segment302and cross-section A-A′ lies above the distribution plate103. The position of the central axis is indicated by center point402.FIG. 4ashows a fluid distribution cap301having a hoof shaped inner element302and an angle profile shaped outer element303. The hatched section304indicates the filler or cover between the inner element302and the outer element303. The hoof shaped cross section401aof the inner element302need not be regular, but may have partially straight walls extending upwards from fluid distribution plate103and arch over to an opposite side of the vent hole113as shown inFIG. 4a.

InFIG. 4bthe inner element302is shown having a circular cross section401bwith a central axis at location402. The edges of the cross-section of the circular inner element302can be aligned and connected to edges of the vent hole113. Other variations of the inner element shape can be contemplated by the skilled person.

FIG. 5shows a fluid distribution cap arrangement500having a fluid distribution plate103with a plurality of fluid distribution caps301in accordance withFIGS. 3aand/or3b. The fluid distribution caps301are arranged over corresponding vent holes113in the fluid distribution plate103in mutually perpendicular directions of their tunnel shaped structure. InFIG. 5it is shown that horizontal components306of fluid outflows from neighboring fluid distribution caps301deflect upwards209contributing to an improved performance when applied in for example the fluidized bed reactor101shown inFIG. 1.

The fluid distribution caps301described above and shown inFIGS. 3a-5have two openings at opposite ends of the fluid distribution cap301to allow fluid outflow. A skilled person may contemplate fluid distribution caps301having a single opening e.g. for example one opening of the fluid distribution cap301as described is closed. Moreover, fluid distribution caps having more than one outflow opening such as Y-shaped fluid distribution caps having three openings or X-shaped fluid distribution caps having four openings may be considered for lower pressure drop in the fluid outflow.

The above described embodiments are given by way of example only. Variations or alterations to the embodiments can be made without limiting the scope of protection as laid down in the claims as set out below.

REFERENCE NUMERALS

103fluid distribution plate

104fluid distribution cap

201apipe segment cap

201bangle profile cap

204apipe segment side wall

204bangle profile side wall

205neighboring pipe segment outflow

207angle profile fluid outflow

208neighboring angle profile outflow

209upward deflected fluid flow

301tunnel shaped fluid distribution cap

304filler or cover

305a,305bflat side wall

306neighboring tunnel shaped fluid distribution cap outflow

401ahoof cross section

401bcircular cross section

402central axis location

500fluid distribution cap arrangement