US2175817A - Distillation of mineral oil - Google Patents

Description

Oct. 10, 1939. c. F. sLAwsoN 2,175,817

DISTILLATION OF MINERAL OIL Original Filed June 25, 1934 N Si Ye l k v DUS N11 Cec///aMSO/l INVENTOR BY R/MW Patented Oct. 10, 1939 UNITED STATES PATENT OFFICE DISTILLATON OF MINERAL OIL Application June 23, 1934, Serial No. 732,004 Renewed March 17, 1938 13 Claims.

This invention relates to the distillation of a composite liquid, and more particularly to the distillation of a hydrocarbon oil.

In the modern practice of petroleum distillation, it is customary to top a crude oil by ashing from a tube still heater into a fractionating tower from which gasoline vapors may be removed overhead, a kerosene distillate as a side stream cut, and heavier residuum from the base of the tower. The kerosene side stream may be stripped with steam in an auxiliary or stripping tower in order to obtain a close cut. While this effectively removes lighter constituents from the kerosene cut, the stripped residue which is generally removed from the base of the auxiliary tower may contain heavier fractions and' impurities which necessitates redistillation or purification treatments. If it is attempted to redistill the kerosene cut within the auxiliary or stripping tower, large quantities of steam may be required such as to render the process uneconomical.

It is an object of the present invention to provide a method of and apparatus for distilling hydrocarbon oil of this character, in which a side 25 stream cut from a primary fractionating tower may be effectively stripped and' redistilled in an auxiliary or stripping tower, to thereby obtain a close clean distillate cut as a side stream from the stripping tower, while at the same time effecting substantial economies in the operation thereof.

It is also modern practice to combine a topping unit of the character described above with a vacuum distillation unit where the heavier or lubricating fractions cf the oil are distilled. This is the so-called atmospheric-vacuum distillation apparatus, in which residuum from the first stage or topping unit is passed through a second stage tube still heater, where it is heated to a high temperature, and then flashed into the vacuum fractionating tower. It is known to withdraw a portion of residuum which has been heated in a second stage heater, and return this heated residuum to the fractionating tower of the first stage, to supply additional heat thereto for distillation purposes. This is objectionable, as the high temperatures of the second stage tube still may result in too high a heat input into the lirst stage fractionating Zone, such that desired flexibility of control is lacking.

Another object oi the present invention is to provide a two stage distillation system of this character, in which additional heat input is provided by recirculating topped crude or residuum to the primary fractionating tower and/or the stripping tower of the rst stage, while affording an independent control of the heat input to secure desired iiexibility of operation.

Briefly, my invention contemplates withdrawing a portion of the reduced crude or residuum of the rst stage, passing it through a separate heating coil where independent control of temperature is aiorded', and introducing heated residuum into the lower portion of the stripping tower to supply the necessary heat for redistillation and stripping therein, thereby obviating the use of objectionable quantities of steam for this purpose. This may be accomplished by withdrawing a portion of the residuurn passing from the rst stage to the vacuum tube still heater, and passing the withdrawn residuum through a separate heating coil, which may be located conveniently in the furnace of the rst stage or topping tube still heater, and then introducing the heated residuum into the stripping tower. Preferably, connections are provided for selectively withdrawing residuum from both the primary and' stripping fractionating towers of the first stage, and for recycling the residuum through the separate heating coil and selectively returning to either or both of the primary and stripping fractionating towers.

Referring to the drawing, in which the single iigure is a diagrammatic illustration of apparatus for carrying out the method of the present invention, vthe rst stage or topping tube still heater is indicated at I0. Oil to be distilled, such as crude oil, is drawn by pump II through pipe l2 and forced under pressure through heating coil I3 positioned within furnace I. The heated oil is then passed by line I4 containing pressure release valve l5, and flashed at I6 into the primary fractionating tower I'l. This tower may be of any suitable conventional construction for refluxing the vapors therein, as by reflux liquid introduced at i8. As shown, the tower is provided with a plurality of decks 0r bubble trays I8, one or more of which may be equipped with a liquid side stream withdrawal 2!) controlled by valve 2|. Uncondensed vapors pass overhead by line 22 to suitable condensers (not shown).

The side stream 2t! is introduced at an intermediate point into the auxiliary or stripping tower 24, which is constructed with a plurality of bubble trays 25 above the zone of introduction of the side stream, and a plurality of staggered baiiies 26 below this zone. trays 25 is equipped with a liquid side stream withdrawal 21 controlled by valve 28.

Residuum is withdrawn from tower l1 by line 30 controlled by valve 3l, and from tower 24 by One or more of the bubble il I) line 32 controlled by valve The residuums from the two towers are combined and drawn through pipe 34 by pump 35, which forces the residuum through line 36 controlled by valve 3l' to a heating coil 38 positioned within the furnace of the second or vacuum stage tube still 3Q. The oil heated in this stage is then discharged through line 45 containing pressure release valve 4I into a vacuum fractionating tower l2 which may be of conventional construction.

Positioned in advance of the second stage tube still 35 is a connection t4 controlled by valve 45, through which a portion of the combined residuum is withdrawn and passed to a heating coil 5:6 positioned within the furnace t@ of the rst stage tube still heater. The coil 45 is preferably located within furnace IQ so that a regulation of the heating eifect of the combustion gases may be obtained, such that an adequate control of the temperature of the heated oil is secured. The heated residuum then discharged through line 4l, and may be selectively introduced into the lower portion of the primary tower il by line 48 containing valve 4?', or into the lower portion of the stripping tower 24 by line 5i? containing valve 5. Line Eil preferably discharges into the stripping tower beneath the bairles 25, as indicated at 52, whereby the bales serve as entrainment separators to remove heavy unvaporized oil from the redistilled vapors passing upwardly through the stripping tower. Additional reflux may be introduced into the stripping 'tower by the line 53, and stripped vapors are returned to the primary tower through the vapor line In operation, crude oil is forced through heating coil I3 of the topping tube still and flashed at I6 into the primary fractionating tower. The lighter constituents including gasoline and kerosene fractions are primarily vaporized, and pass upwardly through the tower countercurrent to descending reflux liquid introduced at I3. Unvaporized liquid passes downwardly through the stripping section of the primary tower, and remaining lighter constituents are vaporized by the heating effect of recycled residuum introduced by line 48. Gasoline may be removed overhead as vapor by line 22 to suitable condensers.

A kerosene fraction is condensed within the tower and removed at 20 as a side stream to the stripping tower 24. 'Hera the kerosene fraction is redistilled by the heating effect of recycled residuum introduced at 52. The kerosene vapors are freed of entrained heavy oil while passing around the entrainment separating baffles 25, and are then reuxed and condensed in the bubble plate section 25 of the stripping tower by reflux introduced at 53. Retained gasoline constituents are effectively stripped and pass overhead by line 54 to the primary tower Il. A close cut kerosene fraction is removed by the side stream 21.

Residuums from both the primary tower Il and the stripping tower 24 are removed by lines 30 and 32, and forced under pressure by pump 35 to lines 36 and 44. The proportion passing to the second stage tube still and the proportion recycled to the separate heating coil 46 are controlled by regulation of valves 3l and 45 respectively.

The recycled topped crude is heated in coil 46 to a temperature approximating the temperature of introduction of the original oil into the primary tower at I6, although this may be varied depending upon the character of distillation desired. For example, the original crude may be heated in the coil I3 to a temperature of about SOW-650 F.; and the recycled residuum may be heated in the coil 45 to a temperature of around 625-675 F. While the coil 4G is shown Vpositioned in the furnace of the topping heater ID, it is to be understood that an entirely separate furnace may be employed for heating the said coil. By suitable control of the quantity of residuum recycled to both the primary and stripping towers I1 and 24, the use of stripping steam may be entirely obviated. However, a proportion of steam may be admitted to the primary tower by the line 56, and to the stripping tower by the line 5l, if desired. The installation provides for substantial exibility of control, due to the independent control of the heating effect of the recycled residuum, the control of the proportion of residuum recycled, and the selective introduction of controlled proportions of reheated residuum into either the primary or stripping towers, or both.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

l. In the non-cracking distillation of hydrocarbon oil, the method which comprises heating the oil in continuously flowing stream and flashing without any substantial cracking thereof into a primary iractionating zone of substantial fractionating capacity, refluxing the vapors therein, removing lighter vapors overhead to suitable condensers, withdrawing an intermediate distillate out which is fractionated to a narrow cut, such as a kerosene fraction, as a side stream to a stripping fractionating zone of lesser fractionating capacity into which no cut lighter than said intermediate distillate cut is introduced, withdrawing bottoms from the stripping fractionating zone, passing withdrawn bottoms in a continuously flowing stream through a heating zone, reti ning the heated bottoms to the stripping fra. ionating zone to supply heat thereto to redistil the said side stream therein and separate it from entrained heavy oil and impurities, fractionating the vaporized side stream and condensing the same within the stripping fractionating :tone as a close distillate cut to separate it from ro' ined lighter constituents, removing the said distillate cut as a side stream from an intermediate point of the stripping fractionating zone, and retur uncondensed vaporized lighter constitts i om the stripping zone to the main fractienating zone.

2. In the non-cracking distillation of hydrocarbon oil, wherein the oil is heated in a continuously flowing stream and ashed without any substantial cracking thereof into a primary fractionating zone where the vapors are reuxed, and an intermediate distillate cut is removed as a side stream to a stripping iractionating zone; the method which comprises withdrawing bottoms from both the primary fractionating zone and the stripping fractionating Zone, combining the bottoms and passing a portion thereof in a continuously flowing stream through a heating zone, returning the heated portion of the bottoms to the stripping fractionating zone to supply heat thereto for stripping purposes, and removing a distillate out as a side stream from an intermediate point of the stripping fractionating zone.

3. In the non-cracking distillation of hydrocarbon oil, wherein the oil is heated in a continuously flowing stream and flashed without any substantial cracking thereof into a primary fractionating zone where the vapors are reiluxed, and an intermediate distillate cut is removed as a side stream to a stripping fractionating zone; the method which comprises withdrawing bottoms from both the primary fractionating zone and the stripping fractionating zone, combining the withdrawn bottoms and passing a portion thereof in a continuously flowing stream through a heating zone, dividing the heated portion of the bottoms and returning a part thereof to the lower portion of the primary fractionating zone and another part thereof to the lower portion of the stripping fractionating zone, and removing a distillate cut as a side stream from an intermediate point of the stripping fractionating zone.

4. In the non-cracking distillation of hydrocarbon oil, the method which comprises heating the oil in a continuously flowing stream and flashing without any substantial cracking thereof into a primary fractionating zone of substantial fractionating capacity, refluxing the vapors therein, removing lighter vapors overhead to suitable condensers, withdrawing an intermediate distillate cut which is fractionated to a narrow cut, such as a kerosene fraction, as a side stream to a stripping fractionating zone of lesser fractionating capacity into which no cut lighter than said intermediate distillate cut is introduced, withdrawing bottoms from the primary fractionating zone, passing at least a portion thereof in a continuously owing stream through a heating Zone, introducing the heated bottoms into the lower portion of the stripping fractionating zone to redistil the said side stream therein and separate it from entrained heavy oil and impurities, fractionating the vaporized sidel stream and condensing the same within the stripping fractionating Zone as a close distillate cut to separate it from retained lighter constituents, removing the said distillate cut as a side stream from an intermediate point of the stripping fractionating zone, and returning uncondensed vaporized lighter constituents from the stripping zone to the main fractionating zone.

5. In the two-stage non-cracking distillation of hydrocarbon oil, in which the oil is heated in the ilrst stage in a continuously ilowing stream and flashed into a primary fractionating Zone, from which residuum is removed and passed in a continuously flowing stream through a second stage heater and then flashed into a vacuum fractionating zone; the method which comprises withdrawing a portion of the residuum from the first stage before it has passed through the second stage heater, passing the residuum thus withdrawn in a continuously flowing stream through a separate heating coil to provide an independent control of the temperature thereof, and returning the said heated residuum to the primary fractionating Zone of the first stage to supply heat for stripping purposes therein.

6. In the two-stage non-cracking distillation of hydrocarbon oil, in which the oil is heated in the first stage in a continuously flowing stream and flashed into a primary fractionating zone, from which an intermediate distillate cut is removed as a side stream to a stripping fractionating zone, and residuum is removed and passed in a continuously flowing stream through a second stage heater and then flashed into a vacuum fractionating zone; the method which comprises returning heated residuum to the lower portion of the stripping fractionating zone to supply heat thereto for stripping purposes.

7. In the two-stage non-cracking distillation of hydrocarbon oil, in which the oil is heated in the ilrst stage in a continuously ilowing stream and flashed into a primary fractionating zone, from which an intermediate distillate cut is removed as a side stream to a stripping fractionating zone, and residuum is removed and passed in a continuously flowing stream through a second stage heater and then flashed into a vacuum fractionating zone; the method which comprises withdrawing a portion of the residuum from the rst stage and passing it in a continuously flowing stream through a separate heating coil to provide an independent control of the temperature thereof, and introducing the heated residuum to the lower portion of the stripping fractionating zone to supply heat for stripping purposes therein.

8. In the two-stage non-cracking distillation of hydrocarbon oil, in which the oil is heated in the first stage in a continuously flowing stream and flashed into a primary fractionating Zone, from which a distillate cut is removed as a side stream to a stripping fractionating zone, and residuum is withdrawn from both the primary fractionating zone and the stripping fractionating zone and combined and passed in a continuously ilowing stream through a second stage heater and then flashed into a vacuum fractionating zone; the method which comprises withdrawing a portion of the combined residuum from the iirst stage before it has passed through the second stage heater, passing the residuum thus withdrawn in a continuously flowing stream through a separate heating coil to provide an independent control of the temperature thereof, and introducing residuum thus heated to the `lower portion of the stripping fractionating zone to supply heat thereto for stripping purposes.

9. In the topping distillation of crude oil, in which the crude oil is heated in a continuously flowing stream and then flashed into a primary fractionating zone, wherein a gasoline fraction is removed overhead, a kerosene fraction is removed as a side stream to a stripping fractionating zone, and a heavier residuum is removed from the lower portion of the primary fractionating zone; the method of obtaining a close kerosene cut which comprises passing a portion of the residuum in a continuously flowing stream through a heating Zone and introducing the heated residuum into the lower portion of the stripping fractionating zone to supply heat thereto to vaporize a substantial portion of the said side stream therein, fractionating the vaporized side stream and condensing a major portion thereof within the stripping fractionating Zone as a distillate kerosene cut, removing the said distillate kerosene cut as a side stream from the stripping fractionating zone, removing heavier oil as residuum from the stripping fractionating zone, and combining the heavier oil with the residuum from the primary fractionating zone.

l0. In non-cracking distillation apparatus of the character described, the combination with a tube still heater flashing into a primary fractionating tower, a stripping tower, and a connection for withdrawing a distillate side stream from the primary tower and introducing it into the stripping tower; of connections for withdrawing residuum selectively from either or both of said towers, a heating coil, means for passing withdrawn residuum from either or both of said u towers. through said heating coil, connections for introducing the said heated residuum selectively to either or both of said towers, and means for withdrawing a side stream cut from said stripping tower.

11. In two stage non-cracking distillation apparatus of the character described, the combination with a first stage tube still heater flashing into a primary fractionating tower, a stripping tower, means for withdrawing a distillate side stream from the primary tower and introducing it into the stripping tower, a second stage tube still heater flashing into a vacuum ractionating tower, and means for passing residuum from the first stage through the second stage tube still and thence into the vacuum tower; of a connection in advance of said second stage tube still heater for withdrawing a portion of the said residuum, a separate heating coil, means for paesing the withdrawn residuum through said separate heating coil, a connection for introducing the heated residuum into the lower portion of said stripping tower, and means for withdrawirg a side stream cut from said stripping tower.

12. In two stage atmospheric-vacuum noncracking distillation apparatus of the character described, the combination with a tube still heat er flashing into a primary atmospheric fractionating tower, a stripping tower, means for withdrawing a distillate side stream from the primary tower and introducing it into said stripping tower, a second stage tube still heater flashing into a vacuum fractionating tower, and means for passing residuum from said first stage through the second stage tube still heater and thence into the Vacuum tower; of means in advance of said second stage tube still heater for withdrawing a portion of the residuum from said rst stage, a

Separate heating coil positioned within the first stage tube still heater, means for passing withdrawn residuum through said separate heating coil, connections for introducing the said heated residuum selectively into either or both or said primary and stripping fractionating towers, and means for withdrawing a side stream cut from said stripping tower.

13. In the non-cracking distillation of hydrocarbon oil, the method which comprises heating the oil in a continuously owing stream and nashing without any substantial cracking thereof into a primary fractionating zone of substantial fractionating capacity, refluxing the vapors therein, removing lighter vapors overhead to suitable condensers, withdrawing an intermediate distillate cut which is fractionated to a narrow cut, such as a kerosene fraction, as a side stream to a stripping fractionating zone of lesser fractionating capacity into which no cut lighter than said intermediate distillate cut is introduced, supplying sufficient heat to the lower portion of the stripping fractionating Zone to redistil the Said side stream therein to separate it from entrained heavy oil and impurities, fractionating the vaporized side stream and condensing the same within the stripping fractionating zone to separate it from retained lighter constituents and produce a distillate cut closely controlled with respect to both its lower boiling and higher boiling ends. removing the said distillate cut as a side stream from an intermediate point of the stripping fractionating zone, and returning uncondensed vaporized lighter constituents from the stripping fractionating zone to the primary fractionating zone.

CECIL FERDINAND SLAWSON.

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