Oil scrubbing column

Abstract

An oil scrub column having a petroleum spirit section and an oil section where each section has mass transfer trays having a plurality of runoff elements that extend parallel to and at a distance from one another, to form angular profiles. The runoff elements have first and second runoff surfaces that converge to form an edge. Scrubbing media introduced onto the edges of the runoff elements flows off via the runoff surfaces at both sides of the edge. The oil section has a greater number of mass transfer trays than the petroleum spirit section. The petroleum spirit section is shorter than the oil section. The mass transfer trays of the petroleum spirit section may be sieve trays, bubble trays or valve trays.

Claims

1. An oil scrub column having a shell which is extended along a longitudinal axis and encloses an interior of the column, the interior being subdivided into a petroleum spirit section and into an oil section, which is arranged below the petroleum spirit section along the longitudinal axis and which is separated from the petroleum spirit section in particular by means of a chimney tray, there being arranged in the petroleum spirit section a plurality of first mass transfer trays and in the oil section a plurality of second mass transfer trays, where the oil scrub column is designed to guide a cracking gas stream through the second mass transfer trays of the oil section and subsequently through the first mass transfer trays of the petroleum spirit section, where the oil scrub column is designed to subject the second mass transfer trays in the oil section to a liquid, hydrocarbon-containing second scrubbing medium, in order to separate out an oil fraction from the cracking gas stream, and where the oil scrub column is designed to subject the first mass transfer trays in the petroleum spirit section to a liquid, hydrocarbon-containing first scrubbing medium, in order to separate out a petroleum spirit fraction from the cracking gas stream, characterized in that the second mass transfer trays each have a plurality of runoff elements extending parallel to and at a distance from one another, in the form of angular profiles, where the runoff elements each have first and second runoff surfaces, where the two runoff surfaces converge along the longitudinal axis towards the petroleum spirit section and meet, to form an edge extending transversely to the longitudinal axis, so that the second scrubbing medium introduced onto the edges of the runoff elements flows off from the respective runoff element via the runoff surfaces at both sides of the respective edge, and where the number of second mass transfer trays in the oil section is greater than the number of first mass transfer trays in the petroleum spirit section, and where the petroleum spirit section has a shorter length along the longitudinal axis than the oil section, and where the first mass transfer trays are designed as sieve trays, bubble trays or valve trays.

2. The oil scrub column according to claim 1, characterized in that the length of the petroleum sprit section is not more than half the length of the oil section.

3. The oil scrub column according to claim 1, characterized in that the petroleum spirit section has 6 to 8 first mass transfer trays.

4. The oil scrub column according to claim 1, characterized in that the oil section is subdivided into a light oil section and into a heavy oil section, which is arranged below the light oil section along the longitudinal axis, there being arranged in each of these sections a plurality of the second mass transfer trays, where the light oil section is separated from the heavy oil section by means of a second chimney tray, and where the oil scrub column is designed to guide the cracking gas stream through the second mass transfer trays of the heavy oil section and subsequently through the second mass transfer trays of the light oil section, where the oil scrub column is designed to subject the second mass transfer trays in the heavy oil section to a liquid, hydrocarbon-containing third scrubbing medium, in order to separate out a heavy oil fraction from the cracking gas stream, and where the oil scrub column is designed to subject the second mass transfer trays in the light oil section to a liquid, hydrocarbon-containing second scrubbing medium, in order to separate out a light oil fraction from the cracking gas stream.

5. The oil scrub column according to claim 1, characterized in that the oil section has 10 to 20 second mass transfer trays.

6. The oil scrub column according to claim 4, characterized in that the light oil section has 6 to 12, second mass transfer trays.

7. The oil scrub column according to claim 4, characterized in that the heavy oil section has 4 to 8 second mass transfer trays.

8. The oil scrub column according to claim 4, characterized in that the oil scrub column has a first liquid distributor, which is arranged in the oil section and which is designed to subject the second mass transfer trays to the second scrubbing medium, where the first liquid distributor is designed to introduce the second scrubbing medium onto the edges of the runoff elements of an uppermost second mass transfer tray of the oil section, so that the second scrubbing medium flows off from the respective runoff element via the runoff surfaces at both sides of the respective edge, where the first liquid distributor is arranged in the light oil section and the uppermost second mass transfer tray is an uppermost second mass transfer tray of the light oil section, and where a second liquid distributor is arranged in the heavy oil section, where the second liquid distributor is designed to subject the second mass transfer trays of the heavy oil section to a third scrubbing medium, and where the second liquid distributor is designed to introduce the third scrubbing medium onto the edges of the runoff elements of an uppermost second mass transfer tray of the heavy oil section, so that the third scrubbing medium flows off from the respective runoff element via the runoff surfaces at both sides of the respective edge.

9. The oil scrub column according to claim 8, characterized in that the first liquid distributor and the second liquid distributor each have a plurality of cutouts through which the respective scrubbing medium can be introduced onto the edges of the runoff elements of the respective uppermost second mass transfer tray, where the cutouts are each arranged perpendicularly above an edge of an assigned runoff element.

10. The oil scrub column according to claim 9, characterized in that the first liquid distributor and the second liquid distributor each have a plurality of final distributor channels which are each extended along said column cross section and also transversely to the runoff elements.

11. The oil scrub column according to claim 10, characterized in that the final distributor channels each have a base which is extended transversely to the longitudinal axis, and two side walls starting from said base, where said side walls each have an upper rim, and where the cutouts are designed in the form of vacancies at the two upper rims.

12. The oil scrub column according to claim 11, characterized in that the first liquid distributor and the second liquid distributor have at least two preliminary distributor channels, which are parallel to one another, are arranged above the final distributor channels along the longitudinal axis and are intended for feeding the final distributor channels with the respective scrubbing medium, where the preliminary distributor channels are extended along the column cross section, and where the preliminary distributor channels extend transversely to the final distributor channels.

13. The oil scrub column according to claim 12, characterized in that the preliminary distributor channels each have a base which is extended transversely to the longitudinal axis, and two side walls starting from said base, where said side walls each have an upper rim, at which cutouts are designed in the form of vacancies via which the respective scrubbing medium can be led into respectively one assigned final distributor channel, where the cutouts of the preliminary distributor channels are arranged in each case perpendicularly above an assigned final distributor channel.

14. The oil scrub column according to claim 12, characterized in that the preliminary distributor channels are connected to one another via at least one compensation channel.

15. The oil scrub column according to claim 3, characterized in that the petroleum spirit section has 7 first mass transfer trays.

16. The oil scrub column according to claim 5, characterized in that the oil section has 16 second mass transfer trays.

17. The oil scrub column according to claim 6, characterized in that the light oil section has 8 second mass transfer trays.

18. The oil scrub column according to claim 4, characterized in that the heavy oil section has 8 second mass transfer trays.

19. The oil scrub column according to claim 11, characterized in that the vacancies are rectangular vacancies.

20. The oil scrub column according to claim 13, characterized in that the of vacancies are rectangular vacancies.

Description

(1) Further details and advantages of the invention will become apparent from the descriptions below of exemplary embodiments by means of the figures:

(2) FIG. 1 shows a schematic sectional view of a prior-art oil scrub column;

(3) FIG. 2 shows a schematic sectional view of an inventive oil scrub column;

(4) FIG. 3 shows a detail from FIG. 2;

(5) FIG. 4 shows the detail IV from FIG. 3;

(6) FIG. 5 shows a plan view of the detail as per FIG. 4;

(7) FIG. 6 shows a partial sectioned view along the line VI-VI in FIG. 5:

(8) FIG. 7 shows a detail view of a fixed bearing of an inventive runoff element;

(9) FIG. 8 shows a selected sectional view of the detail VIII as per FIG. 3;

(10) FIG. 9 shows a plan view of an inventive mass transfer tray and of a liquid distributor for applying a liquid phase to the mass transfer tray;

(11) FIG. 10 shows a selected view along the direction X of FIG. 9 of a compensation channel of the liquid distributor, which joins two preliminary distributor channels of the liquid distributor to one another;

(12) FIG. 11 shows a selected view along the direction XI of FIG. 9 of a final distributor channel with cutouts in the form of rectangular vacancies, which are designed along one rim of a side wall of the final distributor channel;

(13) FIG. 12 shows a selected view along the direction XII of FIG. 9 of a preliminary distributor channel with cutouts in the form of rectangular vacancies, which are designed along one rim of a side wall of the preliminary distributor channel;

(14) FIG. 13 shows a selected, partially sectioned view of a feed pipe for a preliminary distributor channel of a liquid distributor as per FIGS. 9 to 12;

(15) FIG. 14 shows a further selected, partially sectioned view of a feed pipe for a preliminary distributor channel of a liquid distributor as per FIGS. 9 to 13; and

(16) FIGS. 15 to 17 show schematic sectional representations of sieve, bubble cap and valve trays, respectively.

(17) FIG. 1 shows a prior-art oil scrub column 2. The oil scrub column 2 has an upper petroleum spirit section 20 and a lower oil section 21; a cracking gas stream S, produced by steam cracking of a hydrocarbon feedstock (e.g. naphtha) (see above), is passed into a lower region of the oil section 21. In the oil section 21, the cracking gas stream S is subjected in countercurrent to a liquid, hydrocarbon-containing second scrubbing medium W, which in the oil section 21 is applied to second mass transfer trays in the form of single-flow side-to-side baffles 17. As a result, higher-boiling hydrocarbons are separated out from the cracking gas stream S, and collect as oil fraction F in the bottoms 12. In the petroleum spirit section 20, the cracking gas stream S is contacted with a first scrubbing medium W by means of first mass transfer trays, in the form of sieve trays or valve trays 15, to which the liquid, hydrocarbon-containing first scrubbing medium W is applied, in order to separate out from the cracking gas stream S a comparatively lower-boiling petroleum spirit fraction F.

(18) The inventive oil scrub column 1, for its part, is designed so that fouling on the lower first mass transfer trays 15a of the oil scrub column 2 as per FIG. 1 is counteracted.

(19) In detail, the inventive oil scrub column 1 has a substantially cylindrical shell 10, which is extended along a longitudinal axis L coincident with the vertical and which delimits an interior 1 of the oil scrub column 1, which is subdivided along the longitudinal axis L into a petroleum spirit section 20, comprising the top 11 of the oil scrub column 1, and into an oil section 21, which is arranged below it and comprises the bottoms 12 of the oil scrub column 1, said section 21 being subdivided into a light oil section 21a and, arranged beneath it, a heavy oil section 21b. The petroleum spirit section 20 here is separated by a chimney tray 13 from the oil section 21 or light oil section 21a, and the light oil section 21a is separated by a chimney tray 14 from the heavy oil section 21b.

(20) The precooled cracking gas stream S is supplied at a temperature between, for example, about 400 C. and 600 C. to the oil scrub column 1 in the base region of the heavy oil section 21b. The heavy oil section 21b of the oil scrub column 1 has a plurality of second mass transfer trays 100, which are arranged one above another along the longitudinal axis L and are shown in FIGS. 3 to 9. As described above, adjacent second mass transfer trays 100 are each designed so that the runoff elements 101 of each lower second mass transfer tray 100 are arranged centrally below the passages or holes in the second mass transfer tray 100 arranged above it.

(21) The cracking gas S flows through the entire interior of the oil scrub column 1 from bottom to top along the longitudinal axis L of the shell 10 of the column 1; in the heavy oil section 21b, a liquid, hydrocarbon-containing third scrubbing medium W is introduced onto the mass transfer trays 100 by means of a second liquid distributor 300, which is shown in FIGS. 9 to 14 and which is arranged above the mass transfer trays 100 along the longitudinal axis L. The third scrubbing medium W flows down correspondingly in the heavy oil section 21b and is brought into intense contact with the ascending cracking gas stream S by the second mass transfer trays 100. As a result, the fraction of the heaviest hydrocarbons is separated out from the cracking gas stream S, and these hydrocarbons collect as liquid heavy oil fraction F in the bottoms 12 of the oil scrub column 1. From there, the heavy oil fraction F is drawn off, cooled and recycled as a third scrubbing medium W at least partly into the heavy oil section 21b, and is again introduced by means of the second liquid distributor 300 onto an uppermost second mass transfer tray 100 or onto the cracking gas phase S.

(22) From the heavy oil section 21b, the cracking gas stream S, depleted of the heavy oil fraction, passes via the chimney tray 14 into the light oil section 21a of the oil scrub column 1. Here, the cracking gas phase S continues to ascend upward, likewise through second mass transfer trays 100, which are subjected in countercurrent, via a first liquid distributor 200 (see FIGS. 9 to 14) of the light oil section 21a, to a liquid, hydrocarbon-containing second scrubbing medium W, with the result that corresponding lower-boiling hydrocarbons separated out from the gas phase S collect as a liquid light oil fraction in the light oil section 21a, more particularly on the chimney tray 14. From there, this light oil fraction may pass, optionally via runoffs, directly into the preliminary distributor channels 210 of the second liquid distributor 300 of the heavy oil section 21b. Furthermore, said light oil fraction F is drawn off from the light oil section 21a, cooled, and mixed with a petroleum spirit fraction F drawn off from the petroleum spirit section 20, and recycled as the second scrubbing medium W, via said first liquid distributor 200, into the light oil section 21a.

(23) From the light oil section 21a, finally, the cracking gas stream S, depleted of the light oil fraction F, passes via the chimney tray 13 into the petroleum spirit section 20 of the oil scrub column 1, where the cracking gas stream S passes via first mass transfer trays 16, in the form of sieve, bubble cap or valve trays (cf. FIGS. 15 to 17), into the top 11 of the column 1, from where it is drawn off. In the petroleum spirit section 20, the cracking gas stream S is contacted with a liquid, hydrocarbon-containing first scrubbing medium W, which is introduced onto the first mass transfer trays 16, with the consequence that lower-boiling hydrocarbons are separated out from the cracking gas stream S and collect as a liquid petroleum spirit fraction F in the petroleum spirit section 20. The petroleum spirit fraction F is drawn off from the petroleum spirit section 20 and mixed partly with the light oil fraction F drawn off from the light oil section 21a, and is recycled as second scrubbing medium W into the light oil section 21a (see above). Furthermore, a part of the petroleum spirit fraction F may be recycled to a lower first mass transfer tray 16a (e.g. to the second first mass transfer tray 16a from the bottom), in order to increase the circulation on the lower first mass transfer trays 16a, thereby counteracting shifting of the lower first mass transfer trays 16a as a result of formation of polymer (see above).

(24) Along the longitudinal axis L, the petroleum spirit section 20 of the oil scrub column 1 preferably has a length A which is smaller than the length A of the oil section 21, preferably less than half the length A of the oil section 21.

(25) Where the cracking gas S is generated by cracking a feedstock such as naphtha or a lighter feedstock, the heavy oil section 21b can be omitted. In that case an oil fraction F is drawn off from the bottoms 12 of the oil section 21, and is treated in the same way as for the light oil fraction F in the exemplary embodiment above.

(26) FIGS. 3 to 9 show the second mass transfer trays 100 in detail. Generally speaking, mass transfer trays 100 of these kinds can be used advantageously anywhere in columns where there is a high risk of fouling as a result of the liquid or gaseous phases between which mass transfer is to take place.

(27) In accordance with FIG. 9, the second mass transfer trays 100 have a plurality of longitudinally extended runoff elements 101, which are oriented parallel to one another and are extended parallel to the column cross section Q, which extends vertically relative to the longitudinal axis L, at the same height (based on the longitudinal axis L of the shell 10). Adjacent runoff elements 101 here are spaced apart from one another equidistantly and transversely to their direction of longitudinal extent, thus forming a passage or hole between each pair of runoff elements 101, through which gaseous phase S is able to ascend in the interior of the oil scrub column 1.

(28) In accordance with FIGS. 4 to 7 and 9, the runoff elements 101 each have first and second arms 102, 103, which are joined angularly to one another to form an edge 104, so that the runoff elements 101 form equal-armed angular profiles 101. The respective edges 104 of the runoff elements 101 are likewise of longitudinally extended design, and extend parallel to the column cross section Q. Moreover, the arms 102, 103 of the runoff element 101 converge upwardly on one another along the longitudinal axis L, meaning that the two arms 102, 103 of a runoff element 101 each define an upwardly facing runoff surface 102a, 103a, each of which drops downwards, starting from the edge 104 of the respective runoff element 101. If, correspondingly, the respective liquid scrubbing medium W, W is introduced by a first or second liquid distributor 200, 300 onto the respective edge 104 of a runoff element 101, it flows off downwards via the runoff surfaces 102a, 103a at both sides of the respective edge 104, thereby forming two curtains of the scrubbing medium W, W in question.

(29) In accordance with FIG. 8, a plurality of inventive second mass transfer trays 100 are arranged one above another along the longitudinal axis L, the runoff elements 101 of adjacent second mass transfer trays 100 being arranged with an offset relative to one another along the column cross section Q, and so the liquid phase W, W, running off from the runoff surfaces 102a, 103a of the respective runoff element 101 of a second mass transfer tray 100 is introduced onto two runoff elements 101, arranged below this runoff element 101, of an underlying second mass transfer tray 100. Here, the runoff elements 101 of the lower second mass transfer tray 100 in each case are arranged along the column cross section Q, preferably in each case centrally, between two runoff elements 101 of the second mass transfer tray 100 situated above it. The inventive second mass transfer trays 100 are therefore also called cascade trays.

(30) In accordance with FIGS. 4-7, the runoff elements 101 of a second mass transfer tray 100 lie, with mutually opposite end regions 101d (cf. FIG. 7), on an assigned, circulating carrier ring 110, which is fixed in place on an inside of the shell 10 of the oil scrub column 1. Here, one end region 101d in each case is mounted via a fixed bearing, the other via a sliding bearing, on the carrier ring 110.

(31) The runoff elements 101 may be extended comprehensively over the column cross section Q from one inside region of the shell 10 of the oil scrub column 1 to an opposite inside region of the shell 10 of the oil scrub column 1. Also possible, however, is for a runoff element 101 to consist of a plurality of segments 101a, 101b (cf. FIG. 5), which are arranged one after another along the direction of longitudinal extent of the runoff element 101. In this case, gaps between two adjacent segments 101a, 101b may be covered over by a cap 101c. In that case, such segments 101a, 101b lie by their free end regions on the carrier ring 110 and/or on a bearer 112, more particularly a profiled bearer 112, which is extended transversely to the runoff elements 101. Optionally it is possible to provide a plurality of such bearers 112, which in that case extend parallel to one another. One end region of a segment 101a, 101b is then mounted via a fixed bearing on the carrier ring 110 or on a bearer 112, the other end region, respectively, via a sliding bearing.

(32) The bearers 112, where present, engage by one free end region 113 each beneath the carrier ring 110, said region lying on a bearing 111 fixed in place beneath the respective carrier ring 110 on the inside of the shell 10. These end regions 113 of the respective bearer 112 have a vacancy to accommodate the assigned carrier ring 110, and so the respective carrier ring 110, together with the respective bearer 112, forms a substantially stepless surface 112a, on which the runoff elements 101 may lie (cf. FIG. 4). In the case of the bearers 112, in each case, likewise preferably, one end region 113 is mounted via a bearing 111 in the form of a sliding bearing 111 (cf. FIG. 4) on the shell 10, whereas the other end region 113 is mounted via a fixed bearing (cf. FIG. 3).

(33) Furthermore, in accordance with FIG. 9, the second mass transfer trays 100 may each have, to the side of an outermost runoff element 101, a cover element 115, whose purpose is to delimit the passage between said runoff element 101 and the cover element 115 to the envisaged width.

(34) To subject the second mass transfer trays 100, arranged one above another, to the respective liquid scrubbing medium W, W, in accordance with FIGS. 2 and 9-14, a first and/or second liquid distributor 200, 300 is provided. These distributors each have a plurality of upwardly open end distributor channels 202, which are box-shaped in cross section, which are arranged above the respectively assigned second mass transfer trays 100 along the longitudinal axis L of the oil scrub column 1, and which are each extended along said column cross section Q and also transversely to the runoff elements 101.

(35) The longitudinally extended final distributor channels 202 each have a base 203, which is extended parallel to the column cross section Q, and also two side walls 204, said side walls 204 starting from said base 203 and each having an upper rim 205 (cf. FIG. 11), along which cutouts 201 are designed in the form of rectangular vacancies, which along the longitudinal axis L of the respective column 1 are arranged each perpendicularly above an edge 104 of a runoff element 101 assigned to the respective cutout 201. To distribute the liquid phase W, W onto the runoff elements 101, the final distributor channels 202 are then charged with the liquid phase W, W in such a way that it passes over the lower edges 206, extending parallel to the respective tray 203, of the individual cutouts 201 and falls down onto said edges 104, and is distributed further downward by the cascaded runoff elements 101 (cf. FIG. 8), thus forming a multiplicity of curtains of the liquid phase W, W, through which a gaseous phase for treatment (e.g. cracking gas) S is forced in countercurrent, thereby occasioning an intense mass transfer and/or energy transfer between the phases W, W and S.

(36) For the purpose of charging the final distributor channels 202 with the liquid phase W, W, in accordance with FIG. 10, two preliminary distributor channels 210 are provided, which are parallel to one another and are arranged above the final distributor channels 202 along the longitudinal axis L, said channels 210 likewise being designed upwardly open and being box-shaped in cross section. The preliminary distributor channels 210 likewise are extended along the column cross section Q, preferably, in the same way as for the final distributor channels 202, over essentially the entire column cross section, i.e., from one inside region of the shell 10 of the respective column 1 to an opposite inside region of the shell 10. Furthermore, the preliminary distributor channels 210 are extended transversely to the final distributor channels 202.

(37) The preliminary distributor channels 210 likewise each have a base 211, which is extended parallel to the column cross section Q, and also two side walls 212, which start from said base 211 and which each have an upper rim 213, at which cutouts 214 are designed in the form of rectangular vacancies, via which the liquid phase W, W can be passed into one assigned final distributor channel 202 in each case. For this purpose, the cutouts 214 of the preliminary distributor channels 210 are in turn each arranged perpendicularly, along the longitudinal axis L of the shell 10 of the respective column 1, above an assigned final distributor channel 202 (cf. FIGS. 12, 13 and 14).

(38) In accordance with FIGS. 13 and 14, in turn, said preliminary distributor channels 210 are charged, via at least one feed pipe 220, preferably via two feed pipes 220, with the liquid phase F, said pipes 220 extending at least in sections along the longitudinal axis 1, of the shell 10 of the respective column 1; a cutout 221 of the respective feed pipe 220, via which the liquid phase W, W flows from the respective feed pipe 220 into the assigned preliminary distributor channel 210, faces the respective base 211 of the preliminary distributor channel 210 to be supplied, along said longitudinal axis L. Said feed pipes 220 are each arranged between two splash plates 222, which extend parallel to one another and which flank the outlet 221 of the respective feed pipe 220 on either side, and are each fixed in place on an assigned side wall 212 of the preliminary distributor channel 210 in question.

(39) Furthermore, on the outwardly facing outsides of their side walls 212, at both sides of the cutouts 214 of the respective preliminary distributor channel 210, the preliminary distributor channels 210 have a baffle 216, these baffles 216 projecting vertically from the respective side wall 212 and each projecting, by a lower free end region, into the final distributor channel 202 arranged below the respective cutout 214. The baffles 216 serve to guide the flow of the liquid phase W, W from the cutouts 214 of the preliminary distributor channels 210 into the assigned final distributor channels 202.

(40) In order that the liquid phase W, W in the two preliminary distributor channels 210 is always at the same level, the two preliminary distributor channels 210, in accordance with FIGS. 9 and 10, may be joined via at least one compensation channel 215, which is extended between the two preliminary distributor channels 210, specifically transversely with respect to them.

(41) The abovementioned first mass transfer trays 16 (and 16a) of the petroleum spirit section 20 of the oil scrub column 1 are shown schematically in section in FIGS. 15 to 17. Sieve trays 16 as per FIG. 15 are column trays having a downcomer 162, via which the scrubbing medium W passes onto column trays situated beneath. These sieve trays have a plurality of passages 161, through which the cracking gas S flows and contacts the scrubbing medium W located on the respective sieve tray 16.

(42) In the case of first mass transfer trays in the form of bubble cap trays 16, in accordance with FIG. 16, again a downcomer 162 is provided. In the case of bubble cap trays 16, furthermore, said passages 161 are bordered by chimney necks 164, topped off with caps 163, and in particular the chimney necks 164 project into the respectively assigned cap 163.

(43) Valve trays 16, in accordance with FIG. 17, may likewise have a downcomer 162. In the case of valve trays 16, furthermore, said passages 161 can be closed by valves 165, more particularly flaps, in order to prevent downpour. If the cracking gas pressure is sufficient, the valves are forced open, allowing the cracking gas S to flow from bottom to top through the passages 161 of the valve tray. Besides moveable valves, it is also possible to use fixed valves, i.e., fixed valve caps with a promoter effect.