US2067847A - Process for the treatment of hydrocarbon oil - Google Patents

Description

w. w. GARY ET Al.4

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed June 7, 1934 Jan; 12, 1937.

Patented dan. l2, 1937 PROCESS FR THE TREATlWENT OF HYDRUCARBON OIL poration of Delaware Application June 7, 1934, Serial No. 729,386

- 11 Claims.

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

Heretofore it has been proposed to divide crude hydrocarbon oil, by distillation, into a plurality of fractions of different boiling point ranges and separately to crack the fractions having an end point higher than that desired for the final gasoline distillate, to cause the production of a greater amount of products falling in the boiling range of the desired gasoline distillate. it has also been proposed to remove from the crude charging stock a heavy naphtha fraction and to subject this fraction to a reforming heat treatment whereby the anti-knock value thereof is increased, and to introduce the various cracked and reformed products into a single evaporating zone wherein separation thereof into vapors and liquid residue occur; the vapors being separately fractionated to give the iinal desired distillate as well as an intermediate distillate which may be recycled for further cracking. It has also been proposed to utilize two separate evaporating Zones and to introduce the cracked heavier products into one evaporating zone and the cracked intermediate products, i. e. gas oil, in the other evaporating zone in mixture with hot products from the reforming of the heavy naphtha, and to fractionate the resulting vapors tol form the nal light distillate. It has also been proposed to remove liquid residue or cracked tar from the evaporating Zone mentioned, as fuel oil and likewise to dilute such liquid residue or cracked tar with lighter distillates derived from the process in order to form fuel oil of the desired characteristic.

According to the present invention, we have found that improved results may be obtained by modifying the procedure mentioned hereinbefore and introducing the hot products resulting from the reforming treatment of the heavy naphtha directly into an evaporating zone with the cracked or viscosity broken reduced crude, While directing any vapor phase 'cracked products, formed by cracking lighter hydrocarbons, of the nature of gas oil, into a separate evaporating zone from which vapors and liquids are separately withdrawn for further treatment, either alone or in mixture with corresponding products Withdrawn from the evaporator into (Cl. Mii- 49) which the reformed and cracked heavy products are introduced. By virtue of this process, it is possible to reduce the liquid residue or cracked tar resulting from the cracking of the heaviest fraction to a lower gravity than would be possible without the introduction of the hot reformed products into the evaporating zone as mentioned. The hot reformed products aid, both by their contained heat and by their partial pressure efiect, in causing the removal from the heavy products introduced into the evaporating Zone, of lighter constituents as vapors from heavier constituents as liquids. An additional benefit may be secured by preventing the return to the gas oil or clean stock cracking Zone of heavy polymers resulting from the reformation of the heavy naphtha.

In accordance with our invention fresh relatively heavy cracking stock, such as crude, reduced crude or the like, containing both light and heavy constituents, is subjected to a preheating operation, either by indirect heat exchange with products resulting from subsequent cracking, or by passing through a fireheated zone, and is then introduced into a stripping column wherein distillation thereof 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 reduced crude is then 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 not producing extremely large quantities of products in the gasoline boiling range. rihe heavy naphtha is then subjected to a separate heating operation of such character as to improve the anti-knock value thereof and the hot products from the twok 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, an intermediate condensate which is suitable for use as ay clean cracking stock and a heavier condensate suitable for further cracking with the reduced crude.

This 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 nal desired boiling range, e. g. gasoline, and a reiiux condensate which may then be recycled through the third heating zone for further cracking. The light distillate produced by the fractionation of the vapors derived from the two evaporating zones may be 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. In accordance with our invention the fractionation of the vapors from the several evaporating zones, to produce the final desired gasoline distillate, may be carried out in common or separate fractionating zones, or partially in common and partially in separate fractionating zones. It Will ordinarily be preferable in order to avoid du'- plication of apparatus, to utilize a common fractionating zone for this purpose. 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 separate 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 re duced crude cracking coil in a separate furnace.

The above mentioned and further objects and advantages of our 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 our invention.

Referring more particularly to the drawing, reference numeral I 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 l 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 or other hot fluid through line E, 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 3, after having been collected in trap-out trays 9 and Iii, respectively. The remaining uncondensed vapors pass out from the top of the tower through condenser I I wherein they are condensed, and the resulting condensate is collected in receiver I2, which is provided with a drawoff line I3 for the liquid and another drawoff line I4 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 '1, while any unvaporized portions of the introduced charging stock are drawn off through line I5 at the base of the tower.

This liquid last mentioned, e. g. reduced crude, is forced by pump I6 through the coils of viscosity breaking heater Il, 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 I8, having control valve I9, into the evaporator 2i? wherein vapors separate from liquid residue. The resulting vapors pass off through vapor line 2l into partial condenser 22 wherein a portion of the vapors are condensed, the lighter lower boiling fractions remaining uncondensed and passing orf through vapor line 23, either through vapor line 24 to their individual fractionator 25 or through vapor line 26 into the main fractionator 2. The latter method of operation is generally preferable since it requires a lesser amount of equipment, but the individual fractionator 25, when used, has the advantage that the gasoline vapors separated therein may be separately collected.

When the fractionator 25 is used the vapors introduced thereinto 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 It of final 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 3B. Reflux condensate formed in the fractionator 25 is preferably passed through line 3l, 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 viscositybreaking heater I'I, through a line not shown. The partial condensate formed in the partial condenser 22, being in the nature of a heavy gas oil, is preferably returned through line 33, by action of pump 34, to the line I5 for further cracking inA the viscosity-breaking heater I'I. The quantity of such heavy gas oil is greatly increased by the method employed in this process, due to the partial pressures caused by the heavy naphtha, which in the absence thereof Would have remained as liquid in tower 2G and would have been withdrawn from the process through line 55.

The heavy naphtha withdrawn from the stripping column 5 through pipe 8 is forced by pump 35 through the coils of reforming heater 36 wherein 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?, having control valve 33, into the transfer line I8, 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 3l', preferably below the liquid level therein. This introduction of the reformed products into either the transfer line I3 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 I9.

The virgin gas oil withdrawn from the tower through line 1 is forced by pump 39 through the coils of vapor phase heater lill, 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 lll, 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 55, into the evaporator 43, wherein vapors separate from liquid residue. The liquid residue is drawn off through line 56 having control valve 151 and is preferably introduced into flash drum 18, which is held under a considerably lower pressure than that of the evaporator 43, so that partial vaporization of the residue takes place by virtue of its contained heat. The resulting vapors preferably are directed through vapor line G9 into the vapor line 2l, therein commingling with the vapors from the evaporator 2Q, for partial condensation in the partial condenser 22 and further treatment in the fractionator 25. The unvaporized portion is withdrawn through line 5i! and either passed from the system through conduit 5l or combined with the liquid residue formed in the evaporator 20, the latter being withdrawn from the evaporator through line 52 and the combination or blending step being effected by means of crossover line 53 having valve 53. The liquid residue from evaporator 20 may be separately withdrawn through line 55 if desired.

It is, in many instances, advisable to keep the liquid residue from the evaporator 20 and that from evaporator i3 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 36 the liquid residue withdrawn from the evaporator 20 will have a much lower gravity than otherwise. In order that the liquid residues withdrawn from these evaporators may be sold as fuel oil having the necessary qualifications, they may be cut back or blended with lighter condensate stock from other portions cf the system; for example, cycle stock from the fractionator 21 or fractionator 25 may be used. In this connection, attention is directed to our copending application Serial No. 657,186: which covers a process for cutting back such liquid residues or tars.

The vapors pass overhead from the evaporator t3 through line 55 into the fractionator 21, wherein they undergo fractionation in the usual Well known manner, the resultingv fractionated vapors being removed through conduitv 51 and condenser 58, the condensate formed being collected in the receiver 53. This receiver has a liquid drawoff line 60 whereby the gasoline distillate may be removed from the process, and a conventional gas drawoif pipe 6l. 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,

of these vessels, control being effected byby-pass Any other suitable means of ay well-known type may be used for effecting the valves et and 51.

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.

When the fractionator 25 is not used the valve 58 in line 2A is shut and the valve `69 in line 25 is open, thereby causing the vapors from pipe' 23 to pass directly into the fractionator 21 With the vapors from evaporator 43, wherein they undergo fractionation in the same manner as the vapors last mentioned.

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 vaporphase coil located in one furnace and the viscosity-breaking coil located in a separate furnace.

Reference numerals 16 and 11 indicate drawoff lines by means of which reflux condensate may be Withdrawn from the fractionators 14 and 25 respectively, in desired quantities to effect the selected operating conditions. Y 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 place of the partial condenser 22 the evaporator 20 may be provided with a trap-out tray and cooling means to effect par tial condensation of the vapors therein, the condensate being introduced into line 33, if desired.

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 by way of draw-off line 1l.

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 viscositybreaking 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 stripping tower through line 1l if desired, after having been collected on trap-out tray 10. In this type of operation the reduced crude passed through the lviscositybreaking heater will be of considerably higher gravity than in the case where a virgin gasH 011 cut is 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 an East Texas crude charging stock of about 40 A. P. I. gravity light naphtha of about 76 A. P. I. gravity and an endpoint of about 250 F. may be removed from the crude stripping column through condenser il and collected in receiver l2 while the heavy naphtha charged to the reforming heater may be of about 53 A. P. I. gravity and an endpoint of about 440 F. and the reduced crude passed to the viscosity-breaking heater may have a gravity of about` 251 A. P. I. and a fifty per cent point of about 700 vThe average viscosity breaker feed Will have a slightly lower gravity, of for example about 23.5 A. P. I., on account of the recycling to the viscosity-breaker heater of heavy condensate formed in the partial condenser. The gas oil recycled to the vapor phase heater may have a gravity of about 28.0 A. P. I. and an endpoint of about 675 F. If desired a kerosene cut may be removed from the crude stripping column by way of trap-out tray 'l0 and drawoff line 7|; this kerosene having a gravity of, for example, about 42 A. P. I. and an endpoint of about 600 F. The cracking per pass in the viscosity-breaking heater may be about 10% and that in the' vapor phase cracking zone about 18%, while the proportion of reformed naphtha falling in the gasoline boiling range may be about 80% of that charged to the reforming heater. The quantities of products passing through the viscositybreaking heater, vapor phase heater and reforming heater may be in the ratio of about 17 to 20 to 4.

Conditions suitable for the handling of the preceding stock are a viscosity-breaking heater outlet temperature of about 875 F. and a` pressure of about 250 pounds per square inch; a vapor phase cracking heater outlet temperature of about 920 F. and a pressure of about 200 pounds per square inch, and a reformer heater outlet temperature of about 990 F. and apressure of about 750 pounds per square inch, the pressure inl the viscosity-breaking evaporator being about atmospheric and that in the vapor phase cracking evaporator being about 200 pounds per square inch. Under these operating conditions and with the preceding stock a fuel oil of about 12 A. P. I. gravity, a pour-point of F., viscosity at 122 F. of about 42 seconds, a B. S. content of less than 0.4 by centrifugal extraction, may be made by blending by weight 18% of a gas oil condensate cut of say e50-500 F., 20% of cracked tar from the vapor phase evaporator, and 62% of tar from the viscositybreaking evaporator. The gas oil for blending purposes may be obtained from the trap-out tray T4 located. in the lower portion of the fractionator 21, by way of conduit 'I2 having control valve '13, which connects with the drawoif line 5l and with the cross-over line 53. Or reflux condensate from the base of the fractionator may be used, valved line l5 being provided for this purpose. The gravity of the cracked tar or liquid residue withdrawn from the vapor phase flash drum may be, for example, about 6 A. P. I. or higher if desirable, wh' ejthat of the tower 20 may be, for example,

about '41A. P. I.

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, l

the temperature, pressure, and/or gravities being higher or lower as desired.

While we have described a particular embodiment of our 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.

We claim: Y

1. The process of treating relatively heavy hydrocarbon oil for the production of gasoline and other products, which comprises preheating crude hydrocarbon oil to a distilling temperature, introducing the preheatedoil into a stripping zone wherein separation of vapors from liquid residue occurs, fractionally condensing said vapors to form a heavy naphtha condensate and a gas oil condensate, removing the fractionated vapors and condensing them as light naphtha, removing unvaporized reduced crude and passing it through a viscosity breaking cracking zone wherein it is raised to a cracking temperature and subjected to conversion into lighter products, introducing the resulting cracked reduced crude into a first evaporating zone wherein vapors separate from liquid residue, separately removing vapors and residue from said evaporating Zone and subjecting the vapors to fractional condensation to separate therefrom a heavy condensate and an intermediate condensate, separately passing said heavy naphtha condensate through a reforming zone wherein it is subjected to conditions of temperature and pressure such as to improve the antiknock value thereof, introducing the resulting hot reformed products into said rst evaporating Zone to aid in the separating of said cracked products from said viscosity breaking cracking zone into vapors and liquid residue, passing said gas oil condensate through a second cracking zone wherein it is raised to a cracking temperature and subjected to conversion, passing the resulting cracked products into a second evaporating zone wherein vapors separate from liquid residue, separately removing vapors and liquid residue from said second evaporating zone and fractionating the vapors from said rst and said second evaporating zones to separate gasoline therefrom.

2. A process in accordance with claim 1 wherein reuxcondensate formed by the fractionating of said vapors last mentioned and comprising clean cracking stock, is recycled through said second cracking zone for further conversion.

3. A process in accordance with claim 1 wherein the vapors from said rst evaporating zone are fractionated to form a final desired gasoline distillate, an intermediate condensate and a heavy condensate, said heavy condensate is recycled to the viscosity-breaking cracking zone and said intermediate condensate is introduced into said second cracking Zone in mixture with the gas oil derived from said crude charge.

4. A process in accordance with claim 1 wherein the light naphtha derived from the crude charging stock is blended with the gasoline distillate derived from the viscosity-breaking, reforming, and cracking operations.

5. A process in accordance with claim l wherein the liquid residue withdrawn from the said first evaporating zone is blended with a lighter gas oil distillate derived by fractional condensation of cracked vapors formed in the process, in order to create a fuel oil of desired characteristics.

6. A process in accordance with claim 1 wherein the liquid residue from the first and the second evaporators are blended together and with a lighter gas oil distillate derived by fractional condensation of cracked vapors formed in the process, in order to create a fuel oil of desired characteristics.

7. The process of treating hydrocarbon oil which comprises heating crude charging oil to a distilling temperature, separating the resulting heated oil into vapors and a liquid residue of reduced crude, fractionating said vapors to separate therefrom as condensate heavy naphtha, light naphtha and gas oil, passing said reduced crude directly to a first heating zone wherein it is raised to a cracking temperature and subjected to a moderate amount of conversion into lighter products, introducing the resulting cracked products into a first evaporating Zone wherein vapors separate from liquid residue, separately passing said heavy naphtha through a second heating zone wherein it is raised to a temperature suf-- ficient to cause the conversion thereof into gasoline fractions of higher anti-knock value, passing the resulting hot reformed products into said first evaporating zone in mixture with the products from the rst mentioned heating Zone to aid in the separation thereof into vapors and liquid residue, separately removing vapors and liquid residue from said rst evaporating zone,

fractionating said vapors to form a final desired gasoline distillate and an intermediate condensate suitable for use as a clean cracking stock, passing intermediate condensate so formed, in mixture with gas oil from the fractionating operation first mentioned, through a third heating Zone wherein it is raised to a vapor phase cracking temperature and subjected to conversion, introducing the resulting vapor phase cracked products into a second evaporating Zone wherein vapors separate from liquid residue, separately removing vapors and liquid residue from said second evaporating zone and subjecting the vapors to a fractionating operation in order to form a final desired gasoline distillate.

8. A process in accordance with claim 7 wherein a reflux condensate is formed by the fractionation of vapors removed from said' second evaporating zone and this reflux condensate is recycled through the said third heating zone for further cracking.

9. A process in accordance with claim 7 wherein a heavy condensate is formed by the fractionation of the vapors from said first evaporating zone and this heavy condensate is returned to said rst heating zone for further conversion.

10. A process in accordance with claim '7 wherein fractionation of the vapors from said first and said second evaporating zones for the production of the desired gasoline distillate, is carried out in a common fractionating zone.

l1. A process in accordance with claim 7 wherein the light naphtha formed by the distillation step mentioned is blended with the said gasoline distillate to form a nal desired relatively high anti-knock gasoline.

WRIGHT W. GARY. JOHN T. WARD.

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