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1. (WO2014195243) SHAFT REACTOR FOR SOLID-STATE POST-CONDENSATION
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SHAFT REACTOR FOR SOLID-STATE POST-CONDENSATION

Field of the Invention

This invention relates to a shaft reactor for the treatment of bulk material, equipped with internals for lowering the static bed pressure, which substantially consist of vertical plates arranged radially around the geometrical axis of the shaft and in several planes, wherein the plates with one edge are attached to the inside of the reactor wall.

Prior art

Such shaft reactors are known. For example, they serve to post-condense polyester granules. In most cases, the shaft has a cylindrical shape, but for example can also have a square cross-section. The upper end of the shaft usually is terminated by a convex bottom, which is provided with an inlet port for the granules and an outlet port for the gas. The lower end of the apparatus usually forms a conical outlet for the granules. In this region, the supply of the process gas usually also is installed.

The gas, frequently air or nitrogen, flows through the granules with elevated temperature, which can lead to the softening of the polymer. Due to the high temperature and the static pressure in the bed, which is generated by the own weight of the granules, there is a risk of agglutinations of the granules

As is known for example from the patent application CH 689 284 A5, the bed pressure can be lowered by incorporating friction surfaces in the reactor space, which are mounted vertically in flow direction of the granules.

These friction surfaces are mounted so as to be distributed over the height of the reactor in several planes spaced from each other. The spacing between the planes free from internals serves the uniformization of the gas flow over the reactor cross-section in the bed.

Due to the weight of the incorporated friction surfaces, increased demands are imposed on the stability of the reactor. In the known construction, the stability can be ensured alone by the wall of the reactor. In particular in large reactors, the construction costs therefore can greatly be increased, when greater wall thicknesses or more expensive materials such as stainless steel instead of aluminum become necessary.

Therefore, it is the object of the invention to provide a shaft reactor equipped with such internals for lowering the bed pressure, in which the required stability can be achieved with lower costs.

Description of the invention

This object is solved by an apparatus according to the features of claim 1 . Due to the fact that the support tube connects all planes of the friction surfaces of the incorporated plates with each other, the stability of the shaft is improved and the wall of the reactor is relieved. Via its surface and its rubbing effect on the flow of granules, the support tube at the same time also contributes to a lowering of the bed pressure.

An advantageous aspect of the invention is characterized in that the angle at which the plates of a plane are arranged to each other around the support tube, is 90°. This angle corresponds to a number of 4 plates in a plane. This number

forms a good compromise in terms of the lowering of the bed pressure, the stability of the reactor shaft and the construction costs for the reactor.

The number of the plates is not fixed at 4 per plate plane. The number of the plates per plane, the number of the plate planes in the reactor, and also the size of the plates depends on how much friction surface is required for lowering the bed pressure.

The incorporated friction surface also can vary over the height of the reactor. It can be expedient, for example, to incorporate more friction surface in the lower region, so that more plates per plane or larger plates are incorporated there. It is also possible to vary the distance between the planes over the height of the reactor.

Another advantageous aspect of the invention is characterized in that at its ends the support tube each has a conical cap with open tip. The upper end of the support tube protrudes from the bed, wherein the granules inlet expediently lies in the axis of the support tube. The conical shape then ensures that the granules are uniformly distributed around the support tube in the reactor. At the lower end of the support tube, the conical shape leads to the fact that the granules uniformly flow around the tube end and no dead zone is formed. The cone tips can be equipped with openings which serve for the purpose that process gas can flow through the interior space of the support tube as purge gas. This prevents the uncontrolled formation of deposits and condensate in the support tube.

Another advantageous aspect of the invention is characterized in that the tip of the cone located at the upper end of the support tube is covered by a hollow cone such that no granules can get into the support tube, but gas can escape therefrom. The penetration of granules into the support tube should be avoided, as this might lead to uncontrolled deposits and might prevent the gas exchange in the support tube.

Another advantageous aspect of the invention is characterized in that the plates are arranged rotated against each other by an angle around the tube from plane to plane. Due to this measure, the frictional effect of the plates for lowering the bed pressure is uniformly distributed in the bed space. For example, when 9 plate planes are incorporated into the reactor, the angle between two adjacent planes can be calculated with the formula 360 9 = 40°. The angle should be chosen such that in the volume of the shaft the plates or friction surfaces are uniformly distributed in the granules.

Another advantageous aspect of the invention is characterized in that the plates extend with a curvature from the support tube to the shaft wall. Due to this measure, the surface area and hence the rubbing effect of the plates is increased on the one hand, and on the other hand expansions inside the apparatus, as they can occur for example due to changes in temperature, can be compensated.

Another advantageous aspect of the invention is characterized in that on the bottom surface of at least one of the plates a protective envelope extends for accommodating a temperature sensor. Due to this measure, it is possible to install temperature sensors deep down in the interior of the bed, wherein the plate protects them against the bed flowing down.

In another aspect, the invention relates to the use of the reactor according to the invention as solid-state post-condensation reactor (SSP reactor) for the treatment of polymer granules obtained by polycondensation. It is particularly advantageous when the post-condensation reaction proceeds by simultaneously removing the by-products of the post-condensation and/or possibly present impurities. For this purpose, the reactor is charged with an inert purge gas or stripping gas, for example nitrogen, which traverses the bed of granules and in doing so removes the by-products or impurities. In the case of polyester granules, it thus is possible to remove undesired aldehyde groups (so-called dealdehydisation).

Exemplary Embodiments

Further developments, advantages and possible applications of the invention can also be taken from the following description of exemplary embodiments and the drawings. All features described and/or illustrated form the the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

Fig. 1 shows a sectional drawing of a shaft reactor according to the invention. Fig. 2 shows a cross-section through the reactor shaft with the four plates of a plate plane.

Fig. 3 shows a cross-section through the reactor shaft with two adjacent plate planes.

Fig. 4 shows a cross-section through the reactor shaft with the four plates of a plate plane, wherein the plates have a bent shape.

Fig. 5 shows the upper conical end of the support tube 8.

Fig. 6 shows the arrangement of a protective envelope 14 for accommodating a temperature sensor.

Fig. 7 shows a cross-section B-B through the plate 7a and the protective envelope 14.

Fig. 1 shows an example for a cylindrical shaft reactor 1 according to the invention, with inlets and outlets for the granules, 2 and 3, and for the process gas, 4 and 5. The reactor is shown as longitudinal section, so that the internals, in this example consisting of the planes 7 arranged in nine planes 6a to 6i, and the support tube 8.

Fig. 2 shows the cross-section A-A through the reactor 1 with a top view of the plane 6a. There is shown the support tube 8 and the plates 7a-d. In this example, four plates per plane are arranged at an angle of 90° to each other around the support tube 8. The plates each are attached to the support tube 8 and to the wall 9 of the reactor.

Fig. 3 likewise shows the cross-section A-A through the reactor 1 , wherein this top view shows the plane 6a and also the plane 6b. The plates 7 of the plane 6a are shown as continuous line, those of the plane 6b as broken line. There is also shown the angle, in this example chosen with 40°, about which the plates of the plane 6a are rotated against those of the plane 6b, as claimed in claim 5.

Fig. 4 likewise shows a top view of the cross-section A-A of Fig. 1 , wherein here only the plates 7a-d of the plane 6a are shown. In this example the plates are curved, as claimed in claim 6.

Fig. 5 shows the upper conical end of the support tube 8 with the opening 10 for the purge gas exit. The opening 10 is covered by a hollow cone 1 1 against the flow of granules 12. On its bottom surface, the hollow cone 1 1 is provided with openings 13 for the purge gas exit.

Fig. 6 shows the arrangement of a protective envelope 14 for accommodating a temperature sensor, as claimed in claim 7. The protective envelope 14 is directly connected with the bottom surface of the plate 7a. The connection can be made for example by soldering or welding. A thermocouple (not shown) can be introduced into the protective envelope 14 through an opening (not shown) in the reactor wall 9.

Fig. 7 shows a cross-section B-B through the plate 7a and the protective envelope 14, which in this example is designed as tube with round cross-section. There can, however, also be used other, e.g. triangular or rectangular, cross-sectional shapes.

List of Reference Numerals

1 shaft reactor

2 inlet for granules

3 outlet for granules

4 inlet for process gas

5 outlet for process gas

6 a - i, plate planes

7 plates

8 support tube

9 wall of the reactor shaft

10 opening for purge gas exit

1 1 hollow cone for covering the opening 10

12 flow of granules

13 opening for purge gas exit between support tube and hollow cone

14 protective envelope for temperature sensor