US2067869A - Process for the treatment of hydrocarbon oils - Google Patents

Description

.Jan. 12, 1937.

H. V. ATWELL PROCESS FOR THE TREATMENT Of HYDROCARBON OILS Filed July 26, 1934 IN VEN TOR. HAROLD 1 ATWELL ATTORNEY am $E 8 HHH 5 H M. NQ HUM 9wmwmw v a w on on 8 2.

i 2. A ME u mn ||l| Mm .ow HUM \v k 5 Wm mm no 9 @Wu mm WM Q a J m HHH @HE: -u m Patented Jan. 12, 1 937 UETE PATENT OFFEE PROCESS FOR THE TREATMENT OF HYDROCARBON OILS Application July 26, 1934, Serial No. 736,977

4 Claims.

This invention relates to processes for the production of lighter from heavier hydrocarbon oils and pertains more particularly to processes for the treatment of crude or partially reduced 5 crude hydrocarbon oil to form therefrom a final gasoline distillate of relatively high anti-knock value and fuel oil of desired characteristics, as Well as intermediate products if desired.

It is an object of my invention to provide an 10 improved process whereby mainly relatively high anti-knock gasoline may be produced from crude hydrocarbon oil, reduced crude or the like, while at the same time forming separate tar fractions of different characteristics.

More particularly it is an object of my invention to provide an improved process whereby fresh relatively heavy charging stock such as crude hydrocarbon oil is divided into a plurality of distillate fractions and an unvaporized resi- 20 due, these several components being separately cracked, the cracked products from the lightest distillate being combined with the cracked products from the unvaporized residue in one evaporating zone, while the cracked products from the 25 cracking of the intermediate distillate is introduced into a separate evaporating zone, the vapors from the two evaporating zones are separately fractionated to form gasoline distillates and a heavy naphtha fraction from the cracked 30 lightest distillate and from the cracked unvaporized residue being subjected to further conversion of a reforming nature in order to cause the conversion thereof into relatively high anti-knock gasoline constituents, and these products of con- 35 version being introduced into the evaporating zone first mentioned.

In accordance with my invention fresh relatively heavy cracking stock, such as crude, or the like, containing both light and heavy con- 40 stituents, is subjected to a preheating operation, either by indirect heat exchange with products resulting from subsequent cracking, or by passing through a fire-heated zone, and is then introduced into a stripping column wherein dis- 45 tillation occurs with the resulting separation of the heavy stock into a plurality of distillate fractions, for example, light naphtha, heavy naphtha and gas oil, and unvaporized liquid the latter being in the nature of reduced crude. The re- 5 duced crude is subjected to a cracking operation in order to reduce the viscosity thereof so as to form a considerable amount of lighter products suitable for use as clean cracking stock, while at the same time producing some products in 55 the gasoline boiling range. The heavy naphtha is subjected to a separate heating operation of such character as to improve the anti-knock value thereof, and the hot products from the two heating operations are combined in a common evaporating zone, the reformed products being the hotter of the two and serving to aid in the vaporization of lighter constituents from heavier liquid constituents of the reduced crude. The resulting vapors are then subjected to fractionation to form a distillate in the boiling range of the final desired product, preferably having an end point lower than that desired for the final product, e. g. an end point of 300 F. more or less, a light condensate suitable for reformation to form relatively high anti-knockgasoline constituents, an intermediate condensate which is suitable for use as a clean cracking stock and a heavier condensate suitable for further cracking with the reduced crude.

The intermediate condensate is then passed through a third heating zone, and into a separate evaporating zone, either alone or in mixture with an intermediate condensate, such as gas oil, resulting from the stripping of the crude charging stock, and in this heating zone is raised to a cracking temperature and subjected to conversion, preferably in the vapor phase, so that the resulting cracked products, upon fractionation yield a considerable quantity of light distillate in the gasoline boiling range and a reflux condensate which may then be recycled through the third heating zone for further cracking. The light distillates produced by the fractionation of the vapors derived from the two evaporating zones are preferably combined with each other and/or with any light naphtha resulting from the crude stripping operation, to give the final desired high anti-knock gasoline distillate.

By the introduction of the cracked reduced crude and reformed heavy naphtha into a common evaporating zone a low gravity liquid residue or cracked tar is obtained, and this may be brought to the desired specification for use as a fuel oil, by dilution with reflux condensate formed in one of the fractionating steps, this reflux condensate being preferably a light condensate slightly heavier than that returned for further reforming and lighter than that sent to the third heating zone for cracking. In accordance with my invention the separate heating coils for carrying out the heating and cracking steps mentioned hereinbefore may be located in separate furnaces or in the same furnace, or two of them may be placed in one furnace and the other in a sepai lite furnace. A desirable manner of combining the coils would be to place the reforming coil and clean stock cracking coil in one furnace and to place the reduced crude cracking coil in a separate furnace. The above mentioned and further objects and advantages of my invention and the manner of attaining them will be .more fully explained in the following description taken in conjunction with the accompanying drawing. The single figure of the drawing shows diagrammatically a system embodying my invention.

Referring more particularly to the drawing, reference numeral 1 indicates a charging line through which fresh charging stock, such as crude oil, partially topped crude, or the like, is forced by pump 2, thence through heat exchange coils 3 and 4 into the lower portion of stripping tower 5. In the stripping tower the introduced charging stock is subjected to partial vaporization by its contained heat and the vaporization may be aided, if desired, by the injection of steam, gas, or other hot fluid through line B, or by the indirect application of heat in the base of the stripping column. The resulting vapors pass upwardly through the tower and undergo partial fractionation by the action of suitable fractionating elements such as bubble plates or the like, and a plurality of condensate fractions are removed from this stripping column by way of drawoff lines I and 8, after having been collected in trapout trays 9 and [0, respectively. The remaining uncondensed vapors pass out from the top of the tower through condenser H wherein they are condensed, and the resulting condensate is collected in receiver i2, which is provided with a draw-01f line 13 for the liquid and another draw off line M for any gas. The liquid so collected in this receiver may be, for example, a light naphtha. Heavy naphtha is drawn off through the line 8 and gas oil through the line I, while any unvaporized portions of the introduced charging stock are drawn off through line l5 at the base of the' tower.

This liquid last mentioned, e. g. reduced crude, is forced by pump l6 through the coils of viscosity breaking heater I1, wherein the oil is raised to a cracking temperature and subjected to conversion suflicient to form a considerable amount of lighter gas oil charging stock which is suitable for further cracking in the vapor phase. The resulting cracked products pass through transfer line l8, having control valve l9, into the evaporator 20 wherein vapors separate from liquid residue. The resulting vapors pass off through vapor line 2| into fractionator 25.

In fractionator 25 the vapors undergo fractionation in the usual well-known manner, the temperature at the top of the tower being controlled in any conventional way, for example, by an indirect cooling coil (not shown) or by the pumping back of distillate from the receiver 28, which collects condensate resulting from the condensing in condenser 29 of fractionated vapors removed from the fractionator through vapor line 30. Reflux condensate formed in the fractionator 25 is preferably passed through line 3|, by action of pump 32, for combination with the gas oil withdrawn from the stripping column 5 by Way of pipe 1, but part or all of this cycle stock may, if desired, be recycled through the viscosity breaking heater l1, through a line not shown. A heavy partial condensate is preferably formed in the evaporator 20, and collected on trap-out tray 22, being in the nature of a heavy gas oil, and returned through line 33, by action of pump The heavy naphtha withdrawn from the stripping column 5 through pipe 8 is forced by pump 35 through the coils of reforming heater 36 where in it is raised to a reforming temperature and subjected to conditions suitable to cause the conversion thereof into relatively high anti-knock gasoline constituents. The resulting reformed products pass through transfer line 3'1, having control valve 38, into the transfer line l8, wherein they commingle with the cracked products from the viscosity breaking heater and are injected therewith into the evaporator 20. Alternatively the reformed products may be passed directly into the evaporator 20, through line 31, preferably below the liquid level therein. This introduction of the reformed products into either the transfer line It or directly into the evaporator 20, aids very materially in separating the lighter constituents of the viscosity broken products as vapors, from heavier constituents as liquid,'the remaining liquid residue or tar having a much lower gravity, if desired, than it would have in the absence of the hot products from the reforming heater. The combination of the reformed products with the products from the viscosity breaking heater may be made either before or after the latter pass through the control valve I9, but preferably the combination is made before the products pass through the control valve [9.

In order to increase the anti-knock value of the final gasoline distillate, and particularly to reform the heavier ends of the gasoline formed by cracking in the viscosity breaking heater, which gasoline ordinarily has a relatively low anti-knock value, a light reflux condensate is removed from trap-out tray 23, near the top of fractionator 25 and is recycled to the reforming heater 35 through conduit 2% by action of pump 26. The end point of the distillate collected in receiver 28 may be about 300 F. i. e. somewhat lower than that desired for the final product, while the condensate withdrawn from trap-out tray 23 may fall in the boiling range of about 300-500 F., being in the nature of heavy naphtha and including kerosene constituents.

The stock removed from tray 23 will consist mainly of heavy naphtha from the viscosity breaking operation, but will also include recycle stock from the reforming operation. Ordinarily the latter recycle stock is very difiicult to crack because of its coke-forming tendency, although it makes high anti-knock gasoline. However, it will be relatively easy to reform such stock when it is mixed with viscosity breaker naphtha, as would be the case in the present mode of operation. At the same time the viscosity breaker naphtha will be reformed, which is a highly desirable operation.

The virgin gas oil withdrawn from the tower 5 through line I is forced by pump 39 through the coils of vapor phase heater 4i), wherein it is subjected to vapor phase cracking conditions of temperature and pressure such as to cause conversion thereof into lighter products in the gasoline boiling range. The resulting hot products pass through the transfer line 4|, preferably into vapor phase soaking drum 42, but alternatively directly into the evaporator 43 through a valved line not shown. In the vapor phase soaking drum the hot products undergo further cracking substantially in the vapor phase and the resulting cracked products pass through the line 44, having control valve 45, into the evaporator 43, wherein vapors separate from liquid residue. The liquid residue is drawn off through line 46 having control valve 41 and may be diverted from the process as fuel oil or other desired product, or may be subjected to a flashing operation in a separate vessel to form distillate which may be used as a refluxing medium in the several evaporators or fractionators of the system, if desired. The liquid residue from evaporator 20 may be separately withdrawn from the process through lines 52 and 55, but it is preferably diluted with relatively light gas oil condensate withdrawn from tray 63, by means of valved conduits 69, 12 and Alternatively gas oil for blending purposes may be obtained from the trap-out tray 14 located in the lower portion of the fractionator 21, by way of conduit 12. Or reflux condensate from the base of the fractionator 21 may be used, valved line 15 being provided for this purpose. Dilution of the residue or tar from evaporator 29 may likewise be effected by use of a portion of the light condensate from trap-out tray 23, constituting recycle stock for the reformer coil, cross over line 50 being used for this purpose. If desired the residue or tar from evaporator 43 may be blended with that from 20, by a conduit not shown.

It is, in many instances, advisable to keep the liquid residue from the evaporator and that from evaporator 43 separate so that they may be disposed of as individual products possessing different desired characteristics. On account of the distilling effect of the reformed products from the reforming heater 3% the liquid residue withdrawn from the evaporator 20 will have a much lower A. P. I. gravity than otherwise. In order that the liquid residues withdrawn from these evaporators may, if desired, be sold as fuel oil having the necessary qualifications, they may be cut back or blended either before or after aflashing step with lighter condensate stock from other portions of the system; for example, cycle stock from the fractionator 21 or fractionator 25 may be used. In this connection, attention is directed to the copending application Serial No. 657,186 of Gary and Ward which covers a process for cutting back such liquid residues or tars. Preferably, however. a relatively light gas oil condensate is removed from a trap-out tray 68 near the top of fractionator 25, but below trap-out tray 23, and used for cutting back the liquid residues or tars, particularly that removed from evaporator 20 through line 52. The condensate from tray 68 is especially suitable for this purpose since it contains polymers from the reforming of naphtha, which are very "effective diluents.

The vapors pass overhead from the evaporator 43 through line 56 into the fractionator 21, wherein they undergo fractionation in the usual well known manner, the resulting fractionated vapors being removed through conduit 51' and condenser '58, the condensate formed being collected in the receiver 59. This receiver has a liquid drawoff line 63 whereby the gasoline distillate may be removed from the process, and a conventional gas drawoff pipe 6!. A cross-over line 62 is furnished so that the gasoline distillate collected in the receiver 59 may be blended with that collected in the receiver 28. Alternatively, the distillate collected in the receiver 28 may be separamly withdrawn through line 63. Reflux condensate from the fractionator 21 is forced through pipe 64, by action of pump 65, into the line I wherein it is mixed with the gas oil and is again passed through the vapor phase heater for further conversion.

The heat exchange coils 3 and 4 in the fractionator 21 and evaporator 43, respectively, serve to maintain the desired temperature in the tops of these vessels, control being effected by by-pass valves 66 and 61. Any other suitable means of a well-known type may be used for effecting the cooling in these vessels and likewise any other desired means may be provided for pre-heating the crude oil passing to the stripping column 5, for example, indirect heat exchange coils may be placed in the other vessels of the system, or the charging stock may be preheated by a directly fired coil.

The heating of the reduced crude, gas oil and naphtha for viscosity-breaking, vapor phase cracking and reforming, respectively has been described hereinbefore as taking place in separate heating furnaces, but, if desired, some or all of these heating coils could be located in the same furnace, a particularly desirable combination being to have the reforming coil and vapor phase coil located in one furnace and the viscosity breaking coil located in a separate furnace. Also the light condensate withdrawn from tray 23 might be passed through a separate reforming coil, not shown, if desired.

Reference numerals H5 and IT indicate-drawoff lines by means of which reflux condensate may be withdrawn from the fractionators 21 and 25 respectively, in desired quantities to effect the selected operating conditions. If desired reaction chambers or soaking drums may be provided for the cracked products from the viscosity breaking heater and reforming heater, similarly to the vapor phase heater. In the drawing valves shown but not numbered are for obvious control purposes.

In some instances it is desirable to remove a cut of kerosene distillate for disposal without cracking thereof. Such a cut may be removed from the stripper tower trap-out tray 10 by way of draw-off line H.

Another method of operation is to avoid the drawing off of virgin gas oil from the trap-out tray 9 and to supply the vapor phase heater 40 only with cycle stock derived from the viscosity breaking heater and from the vapor phase heater, to the exclusion of the virgin gas oil mentioned. In this case a kerosene cut may be removed from the crude tripping tower through line H if desired, after having been collected on trap-out tray 19. In this type of operation the reduced crude passed through the viscosity breaking heater will be of considerably higher A. P. I. gravity and greater in quantity than in the case where a virgin gas oil out is removed and passed through the vapor phase heater directly.

The cracking temperatures, pressures and other conditions maintained in various parts of the system described hereinbefore, will vary with the character of the charging stock and the character of the final desired product.

When treating a mid-continent crude charging stock of about A. P. I. gravity light naphtha of about 72 A. P. I. gravity and an end pain of about 300 F. may be removed from the crud stripping column through condenser II and col lected in receiver l2 while the heavy naphtha charged to the reforming heater may be of about A. P. I. gravity and an end point of about 500 F. and the reduced crude passed tothe viscosity breaking heater may have a gravity of about 22 A. P. I. and a fifty per cent point of about 700 F. The average viscosity breaker feed will have a slightly lower gravity, of for example about 20 A. P. I. on account of the recycling to the viscosity breaker heater of heavy condensate formed in evaporator 20. The gas oil recycled to the vapor phase heater may have a gravity of about 28.0 A. P. I. and an end point of about 675 F. The cracking per pass in the viscosity breaking heater may be about 10% and that in the vapor phase cracking zone about 20% while the proportion of reformed naphtha falling in the gasoline boiling range may be about 75% ofthat charged to the reforming heater. The quantities of products passing through the viscosity breaking heater, vapor phase heater and reforming heater may be in the ratio of about 20 to 20 to 5.

Conditions suitable for the handling of the preceding stock are a viscosity breaking heater outlet temperature of about 890 F. and a pressure of about 250 pounds per square inch; a vapor phase cracking heater outlet temperature of about 950 F. and a pressure of about 200 pounds per square inch, and a reformer heater outlet temperature of about 1000 F. and a pressure of about 750 pounds per square inch, the pressure in the viscosity breaking evaporator being about atmospheric and that in the vapor phase cracking evaporator being about 200 pounds per square inch.

The preceding temperatures, pressures and other specifications are intended merely to illustrate particularly suitable conditions for treating stock of the character mentioned; but the individual cracking treatments of the several fractions may be carried out with other cracking conditions in accordance with known practice, the temperature, pressure, and/or gravities being higher or lower as desired.

While I have described a particular embodiment of my invention for the purposes of illustration it should be understood that various modifications and adaptations thereof occurring to one skilled in the art, may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The process of treating hydrocarbon oil for the production of relatively high anti-knock gasoline which comprises passing heavy topped crude charging oil from a topping operation directly to a cracking zone wherein it is raised to a moderate cracking temperature and subjected to a moderate amount of conversion of a viscosity breaking nature, introducing the resulting hot cracked products into a vapor separating zone wherein vapors separate from liquid residue, removing said vapors and subjecting them to fractionation in a separate fractionating zone wherein a light reflux condensate in the nature of octane number and anti-knock quality, withdrawing said light condensate from said fractionating zone and passing it through a separate heating zone in mixture with fresh heavy naphtha from an external source, wherein the naphtha mixture is raised to a relatively high cracking temperature and is subjected to reformation with the accompanying formation of relatively high anti-knock gasoline constituents, introducing the resulting hot reformed products into said vapor separating zone in mixture with the hot cracked products from the cracking zone first mentioned, withdrawing said liquid residue from said vapor separating zone, withdrawing said heavy condensate from said fractionating zone and passing it to a separate cracking zone wherein it is raised to a vapor phase cracking temperature and subjected to conversion, introducing the resulting hot vapor phase cracked products into a second vapor separating zone, wherein vapors separate from liquid residue, passing said vapors last mentioned to a second fractionating zone wherein fractional condensation thereof occurs, removing the fractionated vapors from said second fractionating zone and condensing them to form gasoline distillate having the end point desired for the final product, and blending the distillate obtained from the fractionating zone first mentioned with the distillate obtained from the fractionating zone second mentioned to form the final desired gasoline distillate of the desired end point and anti-knock quality.

2. A process in accordance with claim 1 wherein a heavy condensate heavier than suitable for use as clean cracking stock for a vapor phase cracking operation is separated from the vapors separated in said vapor separating zone first mentioned and is recycled to the cracking zone first mentioned for further conversion in mixture with said topped crude.

3. A process in accordance with claim 1 wherein a relatively light condensate, slightly heavier than that returned to the reforming heating zone is separated from the vapors removed from said separating zone first mentioned and is combined with liquid residue removed from said separating zone first mentioned as a diluent to form from said residue a fuel oil of desired low viscosity.

4. A process in accordance with claim 1 wherein said topped crude and said heavy naphtha from an external source are derived by distillation of a common crude petroleum charging stock and wherein a virgin gas oil distillate is derived from said crude charging stock and combined with the condensate passed to said third cracking zone for cracking therewith.

HAROLD V. A'I'WELL.

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