PROCESS FOR THE SEPARATION OF A STREAM COMPRISING VAPOUR AND SOLIDS IN A SEPARATION VESSEL

Abstract

The present invention relates to vapour-solids separations, and in particular provides a process for the separation of a stream comprising vapour and a stream comprising solids from a stream comprising vapour and solids using a separation vessel, said separation vessel having: a. a first inlet for the stream to be separated, b. a liquid outlet, c. a vapour outlet, d. a demister located on the vapour outlet, and e. a second inlet by which liquid can be passed to the demister said process comprising (i) passing the stream comprising vapour and solids through the first inlet and in to the separation vessel, (ii) recovering from the vapour outlet a vapour stream which comprises vapour from the stream comprising vapour and solids and which vapour stream has passed through the demister in the separation vessel, (iii) passing to the separation vessel, via the second inlet, a first liquid stream which contacts the vapour stream in the demister, and (iv) recovering from the liquid outlet a second liquid stream which comprising the solids from the stream comprising vapour and solids, and liquid from the first liquid stream.

Claims

1-12. (canceled)

13. A process for the separation of a stream comprising vapour and a stream comprising solids from a stream comprising vapour and solids using a separation vessel, said separation vessel having: a. a first inlet for the stream to be separated, b. a liquid outlet, c. a vapour outlet, d. a demister located on the vapour outlet, and e. a second inlet by which liquid can be passed to the demister said process comprising (i) passing the stream comprising vapour and solids through the first inlet and in to the separation vessel, (ii) recovering from the vapour outlet a vapour stream which comprises vapour from the stream comprising vapour and solids and which vapour stream has passed through the demister in the separation vessel, (iii) passing to the separation vessel, via the second inlet, a first liquid stream which contacts the vapour stream in the demister, and (iv) recovering from the liquid outlet a second liquid stream which comprising the solids from the stream comprising vapour and solids, and liquid from the first liquid stream, wherein the vapour stream recovered from the vapour outlet is passed to a compressor.

14. A process as claimed in claim 13 wherein the demister is a vane pack demister.

15. A process as claimed in claim 13 wherein the first liquid stream is a fresh liquid stream.

16. A process as claimed in claim 13 wherein the first liquid stream comprises liquid recovered and recycled from the liquid outlet.

17. A process as claimed in claim 13 wherein the stream comprising vapour and solids also comprises liquid, which liquid is recovered in the second liquid stream from the liquid outlet.

18. A process as claimed in claim 13 wherein the stream comprising vapour and solids is a stream from the degassing section of a polymerisation process and the solids are polymer fines.

19. A process according to claim 18 comprising a) passing a polymer containing stream to the degassing section of a polymerisation process and recovering from the degassing section a stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines, b) optionally passing said stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines through a filter to remove some but not all of the polymer fines, c) passing said stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines to a cooler, d) passing said cooled stream through the first inlet and in to the separation vessel.

20. A process according to claim 19 wherein step (c) comprises passing the stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines to a condenser wherein at least a portion of the gaseous condensable component is condensed to form liquid, thereby providing a stream comprising gaseous monomer, a liquid component and polymer fines, which stream comprising gaseous monomer, a liquid component and polymer fines is passed through the first inlet and in to the separation vessel in step (d)

21. A process according to claim 18 wherein the stream from the degassing section of a polymerisation process also comprises one or more organoaluminium compounds.

22. A process as claimed in claim 13 wherein the separation vessel is a tank with the only internals being the demister.

23. An apparatus which comprises a separation vessel having: a. a first inlet for a stream to be separated, b. a liquid outlet, c. a vapour outlet, and d. a demister located on the vapour outlet, characterised in that the separation vessel also comprises a second inlet which is a liquid inlet by which liquid can be passed to the demister, and further wherein the vapour outlet is connected to a compressor such that a vapour stream recovered from the vapour outlet is passed to the compressor.

24. Apparatus according to claim 23 wherein the liquid outlet is connected, externally to the separation vessel, to the second inlet.

25. A process as claimed in claim 14 wherein the first liquid stream is a fresh liquid stream.

26. A process as claimed in claim 14 wherein the first liquid stream comprises liquid recovered and recycled from the liquid outlet.

27. A process as claimed in claim 14 wherein the stream comprising vapour and solids also comprises liquid, which liquid is recovered in the second liquid stream from the liquid outlet.

28. A process as claimed in claim 14 wherein the stream comprising vapour and solids is a stream from the degassing section of a polymerisation process and the solids are polymer fines.

29. A process according to claim 28 comprising a) passing a polymer containing stream to the degassing section of a polymerisation process and recovering from the degassing section a stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines, b) optionally passing said stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines through a filter to remove some but not all of the polymer fines, c) passing said stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines to a cooler, d) passing said cooled stream through the first inlet and in to the separation vessel.

30. A process according to claim 29 wherein step (c) comprises passing the stream comprising gaseous monomer, a gaseous condensable component other than the monomer and polymer fines to a condenser wherein at least a portion of the gaseous condensable component is condensed to form liquid, thereby providing a stream comprising gaseous monomer, a liquid component and polymer fines, which stream comprising gaseous monomer, a liquid component and polymer fines is passed through the first inlet and in to the separation vessel in step (d)

31. A process according to claim 28 wherein the stream from the degassing section of a polymerisation process also comprises one or more organoaluminium compounds.

32. A process as claimed in claim 14 wherein the separation vessel is a tank with the only internals being the demister.

Description

[0064] FIG. 1 is a schematic diagram showing a separation vessel according to the preferred embodiment. In particular, FIG. 1 shows a separation vessel (1) which has a first inlet for a stream to be separated (fed via line 2), a liquid outlet (via line 3), a vapour outlet (via line 4), a demister located on the vapour outlet (5), and a second inlet by which liquid can be passed to the demister (via line 6 and a nozzle 7). As shown in FIG. 1, the second inlet is connected to the liquid outlet, so that a portion of the liquid exiting the separation vessel (1) via the liquid outlet/line 3 can be passed to the second inlet. The remainder of the liquid exiting the separation vessel (I) via the liquid outlet/line 3 is passed via line 8 for further use as required. A pump (not shown) can be provided in the liquid outlet line (3) prior to the separation of the liquid between lines (6) and (8).

[0065] Although not shown, other internals can be present, including a vortex breaker on the vapour outlet and/or one or more baffles to aid distribution of the stream to be separated from the first inlet.

[0066] In the process of the present invention, a stream comprising vapour and solids is passed via line 2 through the first inlet and in to the separation vessel (1). There is recovered from the vapour outlet, via line (4) a vapour stream which comprises vapour from the stream comprising vapour and solids and which vapour stream has passed through the demister (5) in the separation vessel (1). Also passed to the separation vessel, via line 6/the second inlet is a first liquid stream which is sprayed via nozzle (7) onto the demister (5) where it contacts the vapour stream. There is recovered from the liquid outlet, via line 3. a second liquid stream which comprising the solids from the stream comprising vapour and solids, and liquid from the first liquid stream. A portion of this is recycled as the first liquid stream, whilst the remainder is recovered via line 8.

EXAMPLE

[0067] A fluidised bed ethylene polymerisation process with a capacity of 300 ktpa is provided with a separation vessel as shown in FIG. 1.

[0068] A polyethylene containing stream is recovered from a fluidised bed polymerisation reactor and passed to a degassing section from which there is recovered a stream comprising ethylene, comonomer, inert hydrocarbons and polymer fines.

[0069] The stream is passed through a coarse filter designed to remove particles larger than 50 microns, and then cooled. The total polymer fines downstream of the filter may be present at levels up to approximately 1500 ppm by weight.

[0070] The stream, after the coarse filter, is obtained at a rate of approximately 10 te/hr. It is in the vapour phase but comprises approximately 10% by weight of inert hydrocarbons and comonomer which may be partially condensed.

[0071] This stream is passed via line 2 through the first inlet and in to the separation vessel (1). Also passed to the separation vessel, via line 6/the second inlet and a nozzle (7) is a first liquid stream comprising principally inert hydrocarbons and comonomer at a rate of 3.6 te/hr, which contacts the vapour stream in the demister (5).

[0072] There is recovered from the liquid outlet, via line 3, a second liquid stream at a rate of approximately 4.6 te/hr, which comprising the majority of the solids and liquid from the stream comprising vapour, liquid and solids as well as the majority of the liquids from the first liquid stream. 3.6 te/hr of this stream is recycled as the first liquid stream, whilst the remainder, approximately 1 te/hr, is recovered via line 8 including polymer fines.

[0073] There is recovered from the vapour outlet, via line (4) a vapour stream which comprises monomer and isopentane at a rate of approximately 9 te/hr. The solids content of this stream is less than 15 ppm by weight.

[0074] This stream is passed to a compressor where it is compressed for re-use in the process.

Operation of the compressor proceeds without fouling due to fines in the vapour stream.