EP0095792B1 - Process for separating a multi-component liquid - Google Patents
Process for separating a multi-component liquid Download PDFInfo
- Publication number
- EP0095792B1 EP0095792B1 EP83200509A EP83200509A EP0095792B1 EP 0095792 B1 EP0095792 B1 EP 0095792B1 EP 83200509 A EP83200509 A EP 83200509A EP 83200509 A EP83200509 A EP 83200509A EP 0095792 B1 EP0095792 B1 EP 0095792B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- column
- steam
- fraction
- pressure
- liquid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G7/00—Distillation of hydrocarbon oils
Definitions
- the flash tower 5 shown in the drawing is provided with 4 product side withdrawal lines 20.
- the remaining vapour if any is withdrawn over the top of the flash tower 5 via line 7 by the action of the steam ejector system 6.
- the driving steam from the steam ejector system 6 is directly passed together with vapour, if any, from the flash tower 5 via line 21 into a second column 22, hereinafter called stripping tower, which is maintained at a higher sub-atmospheric pressure than the pressure in the flash tower 5.
- the steam passed over the top of the stripping tower 22 is introduced into a plurality of condensers 30, one of which is shown in the drawing, for condensing the steam at substantially atmospheric pressure.
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- Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Description
- The invention relates to a process for separating a multi-component liquid, in particular reduced crude into a plurality of fractions. More specifically the present invention relates to the separation of reduced crude with the objective to maximize the production of valuable distillate fractions and to minimize the production of less valuable residue fraction.
- In normal refinery practice crude oil is first topped to remove gasoline therefrom and optionally other low boiling straight run materials. The residue remaining as bottom product is called reduced crude. Topping of the crude oil is normally carried out in multiple stage fractional distillation columns yielding a top-product and a number of side draw product streams. In such a column the crude oil is flashed in a lower flash zone in the column, whereafter the flashed vapours are fractionated in the upper part of the column. From the reduced crude forming the bottom product from such a fractional distillation column, the main feedstock for catalytic cracking is obtained.
- The most common method for separating this catalytic cracking feedstock from reduced crude is by vacuum flashing.
- Vacuum flashing is a process comprising heating the reduced crude resulting in partial vaporization of the crude to provide a mixture of a liquid phase and a vapour phase, passing the mixture into a lower part of a first column while maintaining a sub-atmospheric pressure within the first column using a steam ejector system, components of the mixture being separated to yield at least one distillate fraction and a bottoms fraction, and withdrawing said fractions from the column. Such a process is disclosed in US-A-3 301 778.
- Due to the important demand for lighter hydrocarbons it is often highly desirable to increase the amount of distillate fractions produced in the flash tower from a given reduced crude feed. This requires flashing off more of the heavier distillate fraction in the feed, resulting in less bottom product. The extent to which more of the heavier distillate fraction can be flashed off is among other things dependent on the degree of reduced pressure in the flash zone of the flash tower. The degree of reduced pressure which can be obtained in the flash zone of the flash tower depends in its turn on the applied steam ejector system and the pressure drop over the internals in the flash tower.
- An object of the present invention is to improve the above-mentioned known process for separating a multi-component liquid, in order to increase the production of distillate fractions from a given feed whilst consuming less energy compared to the known processes.
- To this end the process for separating a multi-component liquid according to the invention is characterized in that it further comprises passing the bottoms fraction to a second column while maintaining a pressure within the second column which is higher than the pressure in the first column, and contacting the bottoms fraction with steam in the second column to obtain at least one heavy-distillate fraction and a residual fraction, wherein driving steam of said steam ejector system is used in the second column for contacting the bottoms fraction.
- In the above described process according to the invention the bottoms fraction from the first column, the flash tower, is stripped with steam in a separate column. Owing to the absence of steam injection in the first column, the pressure in the first column can be maintained at a lower level compared to the pressure, prevailing in systems where flashing and steam stripping are carried out in one column. A lower pressure results in an increased yield of distillate. By using the driving steam of the steam ejector system of the flash tower for stripping the bottoms fraction in the second column, the total amount of required steam can be kept relatively low, allowing a reduction of the costs of the process.
- The invention will now be described by way of example only, with reference to the accompanying drawing showing a schematic representation of a suitable system for carrying out the process according to the invention.
- Reduced crude introduced via line 1 is passed through a plurality of preheaters 2 and a heating furnace 3 where the material is partially vaporized and heated to a transfer temperature of, for example, 425°C. The transfer temperature is preferably the highest temperature to which the residue can be heated without any appreciable cracking, i.e. the incipient cracking temperature. Depending on the composition of the reduced crude this temperature is normally in the range between 400 and 440°C.
- The heated and partially vaporized reduced crude is subsequently passed via a transfer line 4 to a
first column 5, hereinafter called flash tower. The pressure in theflash tower 5 is maintained at a sub-atmospheric level by asteam ejector system 6, communicating with theflash tower 5 via a line 7. A suitable pressure in the flash zone of theflash tower 5 may be in the order of magnitude of about 2.67 kPa (20 mm Hg absolute). Once arrived in theflash tower 5 the heated and partially vaporized reduced crude is forced to flow through a vane type inlet device with a plurality of downwardlyinclined vanes 8, which vanes cause a separation of liquid and vapour. The separated liquid descends to the bottom part 9 and is withdrawn from theflash tower 5 by pump 10 through withdrawal line 11. The separated vapour flows upwardly into the upper section of the flash tower in which ademister mat 12 and a plurality of spray sections 13 are arranged one above the other. - Each spray section 13 is composed of a plurality of
liquid spray nozzles 14 and a draw-offtray 15, and optionally a layer of packing material arranged between thespray nozzles 14 and the accompanying draw-offtray 15, for intensifying the contact between liquid and rising vapour. The draw-offtrays 15 are each provided with openings for the passage of rising vapour and a lower part for collecting descending liquid. The draw-off trays may for example be formed by grid trays or bubble cap trays. The rising vapour after being separated from the liquid upon flowing along thevanes 8, first encounters sprays of liquid from thenozzles 14 of the lowermost spray section 13. Upon contact with the sprays of liquid, liquid remained in the rising vapour is removed therefrom and entrained by the liquid sprays. Thenozzles 14 of the lowermost spray section 13 are supplied with liquid from the draw-off tray of the next upper spray section. Thereto the liquid from the next upper spray section is passed through anaccumulator 16 and is partially recirculated viapump 17 and areturn line 18 to the lowermost spray nozzles 14. Upon passing through thedemister mat 12 arranged above the lowermost spray section 13, any entrained liquid is separated from the vapour so that substantially liquid-free vapour enters the upper region of theflash tower 5. - The vapour passing upward through the
flash tower 5 is gradually condensed in multiple boiling fractions by contact with relatively cool liquid. Thereto, liquid is discharged at several levels from the upper part of theflash tower 5, passed throughcoolers 19 for cooling and reintroduced into theflash tower 5 via thenozzles 14. The upward flow of vapour is contacted with the relatively cool liquid, so that the vapour cools down and is partly condensed. - It has been found that the required heat transfer between the upward vapour flow and the liquid droplets introduced via the
spray nozzles 14 of a spray section 13 takes place within a distance of about 1m. This means that a spray section height of about 1 m will be sufficient for the desired heat transfer between vapour and liquid. Up to now it is normal practice to use spray sections having a height far exceeding 1m. Reduction of the spray section height has the advantage that at a given tower height more spray sections can be installed, and therefore a greater variety of side draw product streams can be obtained. - The
flash tower 5 shown in the drawing is provided with 4 productside withdrawal lines 20. The higher theside withdrawal lines 20 are arranged in theflash tower 5, the lower the boiling points of the withdrawn product streams are. The remaining vapour if any is withdrawn over the top of theflash tower 5 via line 7 by the action of thesteam ejector system 6. The driving steam from thesteam ejector system 6 is directly passed together with vapour, if any, from theflash tower 5 vialine 21 into asecond column 22, hereinafter called stripping tower, which is maintained at a higher sub-atmospheric pressure than the pressure in theflash tower 5. - In the
stripping tower 22 the driving steam is used for stripping the bottoms fraction from the flash tower supplied into saidstripping tower 22 via line 11. Prior to introducing the bottoms fraction into thestripping tower 22, the bottoms fraction is heated in afurnace 23 to bring the bottoms fraction temperature at or near its initial boiling point at the pressure prevailing in thestripping tower 22. The downward flowing bottoms fraction introduced into an upper region of thestripping tower 22 is contacted with the upward flowing steam introduced into a lower region of thestripping tower 22. To guarantee an intimate contact between steam and bottoms fraction, thestripping tower 22 is provided with a plurality ofcontact trays 24, causing a redistribution of the liquid and steam over the cross section of the stripping tower. The contact trays may for example be formed by grid trays, sieve trays or bubble cap trays. - For controlling the temperature in the bottom- part of the tower, the
stripping tower 22 is suitably provided with aquench system 25 containing heat exchange means, for cooling a part of the residual fraction and reintroducing said cooled liquid into the lower part of the column at a level higher than the level of withdrawal. - The upper part of the
stripping tower 22 is provided with aspray section 26 for reintroducing withdrawn cooled liquid into thestripping tower 22 for liquefying the vapour in the top of the column to prevent entrainment of vapour by the steam leaving thestripping tower 22 vialine 27 over the top thereof. - The
stripping tower 22 as shown in the drawing is further provided with twoproduct withdrawal lines - The steam passed over the top of the
stripping tower 22 is introduced into a plurality of condensers 30, one of which is shown in the drawing, for condensing the steam at substantially atmospheric pressure. - The heat obtained from the products withdrawn from the
flash tower 5 and thestripping tower 22 may be applied for preheating the reduced crude to be introduced into theflash tower 5. - Since the steam from the
steam ejector system 6 is at a substantially higher pressure than the pressure in theflash tower 5, the pressure in thestripping tower 22 will also be substantially higher than the flash tower pressure. To obtain the highest possible amount of more valuable heavy distillate fraction and the least possible amount of less valuable residual fraction, the pressure in thestripping tower 22 should however be kept at a low sub-atmospheric pressure. The minimum pressure in thestripping tower 22 is determined by the minimum condensation pressure of the steam leaving thestripping tower 22. - By applying a so-called dry fractionating system - i.e. a system without steam injection - in the flash tower, as shown in the drawing, the pressure in the flash tower can be considerably reduced compared with wet fractionating systems wherein steam is introduced into the flash tower. A lower pressure means in general a higher output of valuable products and less bottom product.
- The present invention is not restricted to a process wherein the initial separation between liquid and vapour in the
flash tower 5 is obtained by causing the reduced crude to flow along a plurality ofvanes 8. Instead thereof, the reduced crude may for example be passed through a centrifugal separator positioned in theflash tower 5. Further the invention is not restricted to the particular arrangement of spray sections, packing material and demister mat as shown in the drawing. The packing material and demister mat can for example be suitably replaced by further spray sections. The number of spray sections is chosen in relation to the number of side products which should be yielded at processing reduced crude with a given composition.
Claims (7)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8215707 | 1982-05-28 | ||
GB8215707 | 1982-05-28 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0095792A2 EP0095792A2 (en) | 1983-12-07 |
EP0095792A3 EP0095792A3 (en) | 1985-10-02 |
EP0095792B1 true EP0095792B1 (en) | 1988-01-13 |
Family
ID=10530713
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP83200509A Expired EP0095792B1 (en) | 1982-05-28 | 1983-04-12 | Process for separating a multi-component liquid |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0095792B1 (en) |
JP (1) | JPS58214302A (en) |
AU (1) | AU555741B2 (en) |
CA (1) | CA1197806A (en) |
DE (1) | DE3375304D1 (en) |
ZA (1) | ZA833819B (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB8903011D0 (en) * | 1989-02-10 | 1989-03-30 | Shell Int Research | Vacuum distillation process |
CH684057A5 (en) * | 1992-11-30 | 1994-07-15 | Buss Ag | Methods for further processing the vacuum residue in a crude oil refinery. |
DE10037774A1 (en) * | 2000-08-03 | 2002-02-14 | Bayer Ag | Method and device for obtaining organic substances from a gas mixture containing these substances |
CN104053751B (en) * | 2012-01-17 | 2017-09-15 | 国际壳牌研究有限公司 | The method of hydrocarbon stream is evaporated in vacuo |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US204707A (en) * | 1878-06-11 | Improvement in vehicle-springs | ||
US2092528A (en) * | 1927-07-28 | 1937-09-07 | Lummus Co | Method of and apparatus for distilling petroleum mixtures |
US3301778A (en) * | 1964-06-15 | 1967-01-31 | Phillips Petroleum Co | Fractional distillation |
US4415443A (en) * | 1981-07-10 | 1983-11-15 | Exxon Research And Engineering Co. | Distillation process |
-
1983
- 1983-04-12 DE DE8383200509T patent/DE3375304D1/en not_active Expired
- 1983-04-12 EP EP83200509A patent/EP0095792B1/en not_active Expired
- 1983-04-12 CA CA000425674A patent/CA1197806A/en not_active Expired
- 1983-05-26 AU AU15003/83A patent/AU555741B2/en not_active Ceased
- 1983-05-26 JP JP58093306A patent/JPS58214302A/en active Granted
- 1983-05-26 ZA ZA833819A patent/ZA833819B/en unknown
Also Published As
Publication number | Publication date |
---|---|
EP0095792A3 (en) | 1985-10-02 |
JPS58214302A (en) | 1983-12-13 |
JPH0512001B2 (en) | 1993-02-17 |
AU1500383A (en) | 1983-12-01 |
AU555741B2 (en) | 1986-10-09 |
ZA833819B (en) | 1984-02-29 |
CA1197806A (en) | 1985-12-10 |
DE3375304D1 (en) | 1988-02-18 |
EP0095792A2 (en) | 1983-12-07 |
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