US2185222A - Cracking hydrocarbon oils - Google Patents

Description

Filed March 26, 1938 C. W. NOFSINGER El' AL CHACKING HYDROCARBON OILS an, 2, 194W..

Patented Jan. 2, 194@ NETE STT@ CRACKING HYDROCARBON OILS Application March 26, 1938, Serial No. 198,216

11 Claims.

This invention relates to the conversion of higher boiling hydrocarbons into lower boiling hydrocarbons and has particular reference to certain improvements in combination cracking processes.

A primary object of the invention is to provide a complete unitary process for processing crude petroleum so as to obtain a maximum yield of gasoline or motor fuel of superior anti-knock quality. The invention contemplates a process in which crude petroleum is distilled to obtain gasoline or naphtha fractions, cendensates of nature of gas oil or kerosene adapted for conversion into gasoline and a petroleum residuum, in which the petroleum residuum is subjected to a primary cracking operation to effect viscosity-breaking, the resultant cracked products separated into vapors and residue and the vapors fractionated to obtain gasoline or nap-htha fractions, an intermediate condensate adapted for conversion into gasoline and a heavy reflux condensate which is subjected to a secondary viscosity-breaking operation and the resultant viscosity-broken products fractionated together with the products from the primary viscosity-breaking operation.

By carrying on the viscosity-breaking operation in two stages, that is, by subjecting the crude residue to a primary viscosity-breaking operation and by subjecting the heavy condensate separated out from the viscosity-broken products to a further viscosity-breaking operation, the yield of intermediate constituents of the nature of gas oil or kerosene adapted for high cracking per pass conditions for conversion into gasoline is greatly increased. In accordance with the invention these intermediate constituents are combined with the cracking stock obtained in the crude oil distillation and subjected to cracking in a separate cracking zone under high cracking per pass conditions to eiect conversion into high antiknock gasoline and a naphtha or gasoline fractien obtained from the viscosity-broken products is combined with a gasoline or naphtha fraction obtained from the crude distillation and subjected to reforming to increase the anti-knock value of the gasoline constituents.

The invention further contemplates the flashing of the residue from the viscosity-breaking operations in a vacuum flash zone wherein the residue is distilled under subatmospheric pressure and the combining of heavy constituents, obtained from. the vapors in the vacuum distillation, with the heavy viscosity-breaker condensate for cracking in the secondary cracking or viscosity-breaking zone. In this way constituents are obtained from the viscosity-broken residue which are of such high boiling point that they cannot be separated by distillation at atmospheric pressure without decomposition and by subjecting these heavy constituents to further cracking in the secondary cracking zone a further yield of intermediate constituents adapted for high cracking per pass cracking is obtained. i

As a feature of the invention, the gasoline or naphtha fractions obtained from the crude dis-v tilling and viscosity-breaking operations, are subjected to cracking in a single-pass cracking zone While the cracking stock condensates of the nature of kerosene or gas oil which are obtained from the crude distilling and viscosity-breaking operations may be subjected to cracking under recycling conditions.

In order to more fully disclose the invention reference will now be had to the accompanying drawing wherein:

Figure 1 is a flow diagram illustrative of the invention; and

Figure 2 is a diagrammatic elevation of the viscosity-breaker evaporator as used in a modification of the invention.

The drawing illustrates a unitary combination cracking unit constituting a practical exemplication ofthe invention. 'Ihe combination unit includes a crude oil stripping tower A, a crude residuum viscosity-breaking coil B, a viscositybreaker evaporator C, a viscosity-breaker fractionating tower D, a secondary viscosity-breaking or heavy gas oil cracking coil E, a vacuum flash drum F, a reforming coil G, a high cracking-perpass cracking coil H, a high pressure evaporator K, a pressure fractionator L, and a pressure flash drum M.

The crude oil charging stock is introduced by pump i@ through a charging line Il. In practice a number of heat exchangers l2 are interposed in the charging line by which the charging stock is preheated by heat exchange with hot products obtained in the unit. The charging line extends to a heating coil i3 positioned in furnace it for supplyingthe additional heat necessary to raise the stock to the desired distilling temperature. Ordinarily suiicient heat for the distillation may be supplied by furnace gases that have been employed in supplying heat to the cracking coils G and I-I. Title charging stock heated to the desired distilling temperature is directed into the stripping and fractionating tower A which separation of vapors from residue takes place and in which the vapors are subjected to fractionation. Since it is generally unnecessary to reform the entire straight-run gasoline, a light gasoline or naphtha fraction is taken off overhead as vapors, condensed in a condenser l5 and collected as a light straight-run distillate in a receiver I6. A heavier fraction of gasoline or naphtha which it is desired to reform is collected as a condensate on a trap-out tray i1v and a higher boiling condensate of the nature of kerosene or gas oil adapted for high temperature cracking for conversion into gasoline is collected in trap-out tray I8. It is frequently desired to recover from the crude oil a kerosene or furnace oil cut and a trap-out tray I9 is indicated for this purpose. In practice the tower A is provided with side-strippers for stripping the reflux condensates withdrawn from the trays l1, I9 and I8 and thus the cut from tray I8 is stripped before being picked up by the pump 5I and the cut from tray i1 is likewise stripped before being picked up by the pump 6I. y

The crude residuum from the tower A is withdrawn through line 20 and directed by pump 2l to the primary viscosity-breaking coil Bi. The coil B is positioned in a furnace 22 adapted for supplying the necessary cracking temperature to effect reduction in the viscosity of the residuum and effect conversion into a large yield of intermediate constituents adapted for high cracking per pass cracking. Temperatures of about 850 F. to 890 F. under 150 pounds to 300 pounds pressure are well adapted for this purpose. The time of reaction in the coil B is limited so as to Secure about 8% to 12% cracking per pass (as measured by conversion into 400 F. end point gasoline).

'Ihe viscosity-broken products are passed through transfer line 23 having valve 24 to the evaporator C in which the pressure is reduced to promote vaporization. It is advantageous to introduce the stream of products from the viscosity-breaking coil onto a tray 25. The pressure in the evaporator C should be reduced to a low order, such as below 60 pounds, in order to insure that substantially all of the lighter constituents will be removed from, the residue before it is directed to the vacuum flashing Zone, which operation will be presently explained. The vapors separated out in the tower C may be subjected to a preliminary dephlegmation, as by means of reflux introduced by line 26. This reux may advantageously consist of heavy condensate from tower D. The vapors are, however, subjected to only a moderate cooling in the evaporator C and are delivered through the vapor line 2l to the fractionating tower D at a` relatively high temperature, such as of the order of 800 F. Since it is ordinarily unnecessary tov reform the lighter gasoline constituents, fractionation is carried on in the tower to form a light gasoline or naphtha fraction which is taken off overhead from the tower as vapors, subjected to condensation in condenser coil 28 and collected as a distillate in a receiver 29. A heavier fraction of gasoline or naphtha adapted for reforming is collected on a trap-out tray 3E). the nature of kerosene or gas oil and adapted for high cracking per pass cracking is collected on a trap-out tray 3l and a still higher boiling condensate is collected in the bottom of the tower. In a typical operation the light distillate collected in receiver 29 will have an end point of about 200 F. to 300 F.; the distillate collected at 30 for reforming will have an end point of about 450 F. to 550 F. and the intermediate fraction collected at 3l will have an end point of about 600 F, to

An intermediate fraction of l '700 F. The heavy reux condensate collected at the bottom of the tower will consist essentially of higher boiling constituents. This heavy condensate is directed by a pump 32 to the cracking coil E, positioned in furnace 33. The oil is subjccted to cracking in the coil E under temperatures of for example 900 F. to 975 F. and under pressures of 200 to 600 pounds with a time of reaction therein to accomplish a cracking per pass (as measured by conversion into 400 F. end point gasoline) of about 12% to 16%. Under these conditions there is a very large conversion into intermediate constituents of the nature of kerosene and light gas oil which are adapted for high cracking per pass conditions. The cracked products pass from the cracking coil E through transfer line 34 having a valve 35 to the evaporator C, being advantageously introduced onto the tray 25. The use of the tray in the tower facilitates the evaporation of the streams introduced into the tower and the evaporating effect may be further increased by the introduction of steam into the tower, preferably directly into the tray. It is generally desirable to quench the stream of cracked products flowing through the transfer line 34 as by means of oil introduced through line 3l.

The residue collecting in evaporator C is withdrawn through line 38 having a valve 39 to the vacuum flash drum F. The distillate in the vacuum still F is carried on under conditions of high vacuum such for example as mm to 90 mm. of mercury absolute pressure. In this way constituents are vaporized which cannot be vaporized at atmospheric pressure without decomposition so as to thus recover an extremely heavy condensate. In the condensing arrangement illustrated, the vapors pass through condensers 40 and 4l and the distillate is collected in receiving drum 42. The desired sub-atmospheric pressure is maintained by a vacuum pump 43 or a barometric condenser may be employed for this purpose. The heavy distillate is withdrawn by a pump 44 and directed through line 45, having a branch 46 extending to the vacuum drum F so that a portion of the condensate may be used for refluxing purposes therein and another branch 41 passing in heat exchange with the condenser coil 40 and extending to the viscosity-breaker fractionating tower D. Steam may advantageously be introduced into the vacuum flash drum F to aid the distillation therein. The temperatures therein will ordinarily be of the order of 700 F. and the condensate collected in the receiving drum 42 will usually have a temperature below 150 F. By passing this condensate in contact with the hot vapors leaving the drum F the temperature of the condensate may be raised to a temperature of the order of 600 F. so that the condensate may be introduced into a lower section of the tower D, preferably below the trap--out tray 3|, without unduly reducing the temperature therein. The heavy condensate thus introduced intothe tower is subjected to the fractionating conditions therein, the unvaporized portions being collected with the reflux condensate at the bottom of the tower for passage to the recycling cracking coil E. The heavy constituents produced in the vacuum distillation of the viscositybreaker residue are thus combined with the heavy condensate formed from the vapors from the viscosity-breaker evaporator C and the combined constituents subjected to cracking to thus increase the yield of kerosene or gas oil constituents adapted for high cracking per pass cracking. In other words, the intermediate constituents which are formed in the primary viscositybreaking coil B and in the recycling cracking coil E are accumulated in the viscosity-breaker iractionator D, being collected at 3l, for passage to the high cracking per pass cracking coil as will be presently explained. The heavy residue produced io the vacuum distillation is withdrawn from. the drum F by pump d8.

The straight-run cracking stock collected on tray lil of tower A is withdrawn through a line i0 and the intermediate fraction collected on tray or tower D is withdrawn through line 50 and the condensates are conducted by pump l through a line 52 to the tower L. Vapors from the separator pass through vapor line 53 into the tower L and are dephlegmated therein by the combined straight-run and viscosity-breaker distiliates which are introduced into the tower. The evaporator K may be supplied with a reflux introduced through line 54 in order to insure that the condensate collecting in tower L will be of a clean character adapted for high crack per pass cracking. Unvaporized constituents of the introduced condensates and reflux condensate formed from the condensed vapors is withdrawn from the tower L by pump 55 and directed into the cracking coii H positioned in furnace 5t. The oil in the cracking coil I-I is subjected to cracking temperatures of, for example, 950 F. to 1050" F. under 400 pounds pressure or higher with a time of reaction adapted to sustain a cracking per pass (as measured by conversion into l400 1?. end point gasoline) of about 20% to 30%. Due to the fact that the cycle constituents (constituents that have been subjected to previous cracking) contained in the reflux condensate in the tower L are diluted with relatively large quantities of the straight-run stock from tower A as well as with relatively large quantities of condensate from the viscosity-breaker fractionator D the greater portion of which condensate has been subjected to less extensive cracking than that which takes place in the cracking coil i-I, it is possible to maintain a relatively high allowable cracking per pass in the cracking coil H so as to eiiect conversion into high anti-knock gasoline constituents. The cracked products from the cracking coil H pass through transfer line 5'! having a valve 58 to the separator K, the pressure being preferably reduced in the separator although maintained under a superatmospheric pressure usually not below about 200 lbs.

The straight-run gasoline or naphtha fraction collected in tray ii of tower A is withdrawn through a line 59 and the viscosity-breaker gasoline or naphtha fraction which has been segrem gated for reforming in tray 30 is withdrawn through line Sli and these gasoline or naphtha fractions are directed by a pump iii through a line t2 to the reforming coil G positioned in furnace The gasoline or naphtha fractions are subjected in the coil G to a temperature suii"i cient to eiiect reforming and preferably to temperatures of 950 F. to 1.050 F. under pressures upwards of 400 pounds with a time of reaction adequate to effect the desired increase in antiknock duality. The stream of reformed products from the cracking coil G passes through transfer line ik'l, having a valve 05, to the separator K.. it is generally desirable to quench the cracking streams from both cracking coils G and H to re duce the temperature somewhat and a line iid is indicated. for introducing a cooling or flushing agent to the transfer line 64 and a line lil is indcated for introducing a cooling or ilushing agent into the stream of products in the transfer line 5l. The oil introduced through lines S6 and El may consist of condensate oil obtained in some part of the combination cracking unit.

Residue is withdrawn from the high pressure evaporator K' through a line 68 having a Valve and directed into a reduced pressure flash drum M wherein the residue is subjected to dash distillation. A line l0 is indicated for supplying reiiux to the flash drum. The separated vapors pass through vapor line li to the fractionator D of the viscosity-breaking unit so that the vapors may thus be subjected to fractionation in the tower D, together with the vapors from the evaporator C, and the flashed constituents directed to the cracking coils. The flashed residue is withdrawn through line 12.

The light viscosity-breaker distillate collected in receiver 29 is advantageously directed by a pump 'i3 through line It and refiuXe-d in the tower L. The light gasoline constituents from the viscosity-breaking operation may thus be combined with the cracked gasoline constituents which are taken oiT the tower L. The vapors from the tower L may be condensed in a condenser 'l5 and the distillate collected in receiver i6 to constitute the final desired gasoline product of the process.

In the modication of the invention illustrated in Figure 2 the line 3d from the heavy ges oil cracking coil E may, instead of discharging onto the tray 25, discharge onto a superposed tray di; so that the cracked products from the cracking coil E may be subjected to evaporation to produce a separate residue. An additional trap-out tray 30a below the tray 30 is provided for collecting a separate residue to be withdrawn through a line 35h. The residue containing the residual constituents from the cracking coil B may then be separately withdrawn through line 3B and conducted to the vacuum flasher F while the separate residue withdrawn from the tray 36a may be separately withdrawn and may advantageously be passed to the iiasher M. Thus in the modifled operation only the residue from the primary viscosity-breaking operation is .passed to the vacuum flasher and residual constituents from the heavy gas oil cracking coil E are combined in the higher pressure flasher M with residual constituents from the evaporator K. In this operation the vapors from flash drum M pass through. vapor line 'll to the fractionating tower D so that the desired concentration of gas oil constituents in the tower D, adapted for passage toy the cracking coil H, is maintained.

In a typical operation in accordance with the invention, an East Texas crude oil of 39.3 A. P. I. gravity is distilled and fractionated in tower A and a reduced crude of 23.7 A. P. I. gravity i" withdrawn and passed to the viscosity-breaking coil B. The reduced crude is introduced to the cracking coil under a pressure of 410 pounds and is delivered from the coil at a temperature of 860 F. under 100 pounds pressure. The evaporator C is held at 45 pounds pressure with a temperature of 810 F. in the lower portion thereof. The bottom of tower D is at a temperature of '700 F. and heavy reux condensate is with-drawn by pump 32 and introduced at 745 pounds pressure to the heavy gas oil cracking coil E. The cracked products are delivered from this cracking coil at a temperature of 930 F. under a pressure of 500 pounds and the stream is quenched to 900 F. before delivery to the evaporator C.

Residue consisting of residual constituents from cracking coils B and E is withdrawn from the tower C and subjected to flash distillation in tower F under mm. of mercury absolute pressure with a temperature of 710 F. in the lower portion of the tower. The heavy vacuum ashed distillate is collected in receiver 42 at a temperature of F. This distillate has a gravity of 18.2 A, P. I. and has a 10% distillation point of 632 F. This distillate, except for a portion thereof which is refluxed on the tower F, is preheated by contact with the vapors passing through coil 40 and is delivered through line 4l to the tower D at a temperature of 475 F.

A virgin light gas oil cut having an end point of 650 F. is withdrawn from tray I8 of tower A and combined with a gas oil cut having an end point of 685 F., withdrawn from tray 3| of tower D. The mixed gas oils are refluxed on the high pressure fractionating tower L, and reflux condensate withdrawn from tower L at a temperature of 695 F. is introduced at a pressure of 1185 pounds to the cracking coil H. The cracked products are delivered from the cracking coil I-I at a temperature of 950 F., under a pressure of 750 pounds, and the stream is quenched to 845 F. before delivery to the evaporator K. The evaporator is held under 245 pounds pressure with a temperature of 780 F. in the lower part thereof.

A naphtha cut having an initial boiling point of 220 F. and an end point of 546 F. is Withdrawn from tray l1 of tower A and combined with a naphtha cut withdrawn from tray 30 of tower D, having an initial boiling point of 206 F. and an end point of 502 F. The mixed naphtha stocks are introduced to the reforming coil G under pressure of 1030 pounds and the cracked products are delivered from the coil G at a teinperature of 975 F, under a pressure of 750 pounds. The stream is quenched to a temperature of 850 F. before delivery to the evaporator K. Residue from the evaporator K is flash distilled in tower M at 44 pounds pressure at a temperature of 740 F., the vapors from the tower passing at a temperature of 660 F. to the tower D.

In this typical run the straight-run gasoline, collected in receiver I6, after depropanization constitutes 30.3% of the charging stock and the cracked gasoline product, collected in receiver 16, after being subjected to clay treating and stabilization constitutes 31.27% of the charging stock, thus giving a total yield of gasoline of 61.57%. The gasoline is of 68 octane number (C. F. R. Method). In addition to the gasoline product, 7.12% of furnace oil and 23.75% of fuel oil is made.

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

We claim:

l.. In the cracking of hydrocarbon oils, the process which comprises subjecting crude petroleum to vaporization in a primary separating zone to form vapors and residue, subjecting the separated vapors in a ilrst fractionating zone to fractionation to separate a fraction comprising gasoline constituents from higher boiling constituents, passing said residue to a primary cracking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a second separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a second fractionating zone and subjecting vapors therein to fractionation to form a heavy reflux condensate, passing said heavy reux condensate to a second cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said second separating zone, subjecting vapors in the second fractionating zoneA to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, combining said fractions containing gasoline constituents obtained from the rst and second fractionating zones and directing the mixed fractions to a reforming zone wherein the mixture is subjected to cracking temperature adequate to effect reforming of the gasoline constituents into constituents of increased anti-knock value, separating resultant reformed products, separately from the previously nientioned separating and fractionating zones, to form residue and evolved vapors, fractionating said evolved vapors in a third fractionating zone to separate a light distillate from higher boiling condensate, combining higher boiling constituents thus obtained with higher boiling constituents obtained from the first fractionating zone and with intermediate constituents obtained from the second fractionating zone and directing the mixture to a recycling cracking Zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant cracked products to form residue and evolved vapors and fractionating the evolved vapors in said third fractionating zone.

2, In the cracking of hydrocarbon oils, the process which comprises subjecting crude petroleum to vaporization in a primary separating zone to form vapors and residue, subjecting the separated vapors in a rst fractionating zone to fractionation to form a fraction containing gasoline constituents and a higher boiling condensate, passing said residue to a primary cracking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of high yield of intermediate constituents adapted for conversion into gasoline,

directing the viscosity-broken products into 'a second separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a second fractionating zone and subjecting the vapors therein to fractionation to form a heavy reflux condensate, an intermediate condensate and a lighter fraction cornprising gasoline constituents, passing said heavy reflux condensate to a second cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said second separating zone, combining said fractions cornprising gasoline constituents obtained from the rst and second fractionating zones and directing the mixed fractions to a reforming zone wherein the mixture is subjected to cracking tem- 'Ill perature adequatev to effect reforming of the gasoline constituents into constituents of increased anti-knock value, directing resultant reformed products into a third separating zone wherein separation of `residue from vapors takes place, passing said separated vapors into a third fractionating zone, introducing into said third fractionating Zone said higher boiling condensate obtained from the first fractionating zone an-d said intermediate condensate obtained from the second fractionating zone and subjecting the constituents in the third fractionating zone to fractionation to form light distillate and higher boiling reflux condensate containing constituents derived from the first and second fractionating zones, directing said reflux condensate to a recycling cracking Zone wherein the reflux `condensate is subjected to high cracking ternperature under conditions to effect conversion into gasoline 4constituents of high anti-knock quality, and passing resultant cracked products from the recycling cracking zone into said third separating zone.

3. In the cracking of hydrocarbon oils, the process which comprises subjecting crude petroleum to vaporization in a primary separating zone to form vapors and residue, subjecting the separated vapors in a first fractionating zone to fractionation to separate a fraction comprising gasoline constituents from higher boiling constituents, passing said residue to a primary cracking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscositybroken products into a second separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a second fractionating zone and subjecting vapors therein to fractionation to form a heavy reflux condensate, passing said heavy reiux condensate to a second cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said second separating zone, subjecting vapors in the second fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, combining said fractions containing gasoline constituents obtained from the first and second fractionating zones and directing the mixed fractions to a reforming zone wherein the mixture is subjected to cracking temperature adequate to effect reforming of the gasoline constitutents into constituents of increased antiknock value, combining higher boiling constituents obtained from the first fractionating zone with intermediate constituents obtained from the second fractionating zone and directing the mixture to a cracking Zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the cracked products from the latter cracking zone and the reformed products from said reforming zone into vapors and residual products and fractionating the evolved vapors to recover a desired gasoline distillate.

4. In the cracking of hydrocarbon oils, the process which comprises subjecting crude petroleum to vaporization in a primary separating zone to form vapors and residue, subjecting the separated vapors in a first fractionating zone to fractionation to separate a fraction comprising gasoline constituents from higher boiling constituents, passing said residue to a primary cracking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscositybroken products into a second separating Zone wherein separation of vapors from liquid residue takes place, passing the separated vapors into a second fractionating zone and subjecting vapors therein to fractionation to form a heavy reux condensate, passing said heavy reflux condensate to asecond cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone in'to said second separating zone, subjecting vapors in the second fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, withdrawing liquid residue from said second separating Zone and subjecting it to vacuum distillation in a flashing zone held under sub-atmospheric pressure to form a heavy vacuum distillate and introducing said heavy vacuum distillate into said second fractionating zone so that any portion of the vacuum distillate remaining lunvaporized after contact with the vapors undergoing fractionation will be charged to said second cracking zone with said heavy reiiux condensate, combining said fractions containing gasoline constituents obtained from the first :and second fractionating zones and directing the mixed fractions to a reforming zone wherein the mixture is subjected to cracking temperature adequate to effect reforming of the gasoline constituents into constituents of increased anti-knock value, separating resultant reformed products separately from the previously mentioned separating and fractionating Zones to form residue and evolved vapors, fractionating said evolved vapors in a third fractionating zone to separate lighter fractions from higher boiling constituents, combining higher boiling constituents thus obtained with higher boiling constituents obtained from the first fractionating zone and with intermediate constituents obtained from the second fractionating zone and directing the mixture to a recycling cracking zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant cracked products to form residue and evolved vapors and fractionating the evolved vapors in said third fractionating Zone.

5. In the cracking of hydrocarbon oils, the process which comprises subjecting crude petroleum to vaporization in a primary separating zone to form vapors and residue, subjecting the separated vapors in a first fractionating zone to fractionation to separate a fraction comprising gasoline constituents from higher boiling constituents, passing said residue to a primary cracking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a second Separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a second fractionating zone and subjecting the vapors therein to fractionation to separate as condensate heavy constituents from vapors, withdrawing liquid residue from said second separating Zone and subjecting it to vacuum distillation in a flashing Zone held under sub-atmospheric pressure, combining heavy constituents recovered from the vapors in second cracking Zone into said second separating zone, subjecting vapors in the second fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, combining said fractions containing gasoline constituents obtained from the first and second fractionating zones and directing the mixed fractions to a reforming zone wherein the mixture is subjected to cracking temperature adequate to effect reforming of the gaso- Vline constituents into constituents of increased antiknock value, separating resultant reformed products, separately from the previously mentioned separating and fractionating Zones, to form residue and evolved vapors, fractionating said evolved vapors in a third fractionating zone to separate a light distillate from higher boiling constituents, combining higher boiling constituents thus obtained with higher boiling constituents obtained from the rst fractionating zone and with intermediate constituents obtained from the second fractionating zone and directing the mixture to a recycling cracking Zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant cracked products to form residue and evolved vapors and fractionating the evolved vapors in said third fractionating zone.

6. In the cracking of hydrocarbon oils, the process which comprises introducing a petroleum residual stock into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a first separating zone wherein separation of vapors from liquid residue takes place, passing the separated vapors into a rst fractionating zone wherein the vapors are subjected to fractionation to form a heavy reux condensate, passing said heavy reflux condensate to a second cracking Zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said first separating Zone, subjecting vapors in the rst fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, directing said fraction cornprising gasoline constituents to a single-pass reforming Zone wherein the gasoline constituents are subjected to cracking temperature adequate to effect reforming into constituents of increased anti-knock value, separating resultant reformed products, separately from the previously mentioned separating and fractionating zones, to

form residuey and evolved vapors, fractionating' said evolved vapors in a second fractionating zone to separate a light distillate from higher boiling constituents, combining higher boilingconstituents thus obtained with intermediate constituents obtained from the rst fractionating zone and directing the mixture to a recycling cracking zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant cracked products to form residue and evolved vapors and fractionating the evolved vapors in said second fractionating Zone.

'7. In the cracking of hydrocarbon oils, the process which comprises introducing a petroleum residual stock into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a rst separating zone wherein separation of vapors from liquid residue takes place, passing the separated vapors into a first fractionating zone wherein the vapors are subjected'to fractionation to form a heavy reflux condensate, passing said heavy reflux condensate to a second cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said first separating zone, withdrawing liquid residue from said iirst separating zone and subjecting it to vacuum distillation in a flashing Zone held under sub-atmospheric pressure to form a heavy vacuum distillate and introducing said heavyA vacuum distillate into said rst fractionating zone so that any portion of the vacuum distillate remaining unvaporized after Contact with the vapors undergoing fractionation will be charged to said second cracking zone with said heavy reflux condensate, subjecting vapors in the rst fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, directing said fraction comprising gasoline constituents to a single-pass reforming Zone wherein the gasoline constituents are subjected to cracking temperature adequate to effect reforming into constituents of increased antiknock value, separating resultant reformed products separately from the previously-mentioned the mixture is subjected to a high cracking tern-v perature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant'cracked products to form residue and evolved vapors and fractionating the evolved vapors in said second fractionating zone. l

8. In the cracking of hydrocarbon oils, the

process which comprises introducing a petroleumv itill residual stock into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a first separating Zone wherein separation of vapors from liquid residue takes place, passing the separated vapors into a first fractionating zone and subjecting the vapors therein to fractionation to separate as condensate heavy constituents from vapors, withdrawing liquid residue from said second separating zone. and subjecting it to vacuum distillation in a flashing zone held under subatmospheric pressure, combining heavy constituents recovered from the vapors in the vacuum distillation with heavy constituents formed in said first fractionating zone and passing the combined constituents to a second cracking Zone wherein the mixture is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked roducts from the second cracking zone into said first separating zone, subjecting vapors in the first fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, directsaid fraction comprising gasoline constituents to a single-pass reforming zone wherein the gasoline constituents are subjected to cracking temperature adequate to effect reforming into constituents of increased anti-knock value, separating resultant reformed products separately from the previously mentioned separating and fractionating zones to form residue and evolved vapors, fractionating said evolved vapors in a second fractionating Zone to separate a light distillate frorn higher boiling constituents, combining higher boiling constituents thus obtained with intermediate constituents obtained from the first fractionating zone and directing the mixture to a recycling cracking zone wherein the mixture is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, separating the resultant cracked products to form residue and evolved vapors and fractionating the evolved vapors in said second fractionating zone.

9. In the cracking of hydrocarbon oils, the process which comprises introducing a petroleum residual stock into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a first separating zone wherein separation of vapors from liquid residue takes place, passing the separated vapors into a first fractionating zone and subjecting the vapors therein to fractionation to form a heavy reiiux condensate, an intermediate condensate and a lighter fraction comprising gasoline constituents, passing said heavy reflux condensate to a second cracking zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking zone into said first separating Zone, withdrawing liquid residue from said first separating zone and subjecting it to vacuum distillation in a ashing Zone held under sub-atmospheric` pressure to form a heavy vacuum distillate and introducing said heavy vacuum distillate into said first fractionating zone so that any portion of the vacuum distillate remaining unvaporized after contact with the vapors undergoing fractionation will be charged to said' second cracking zone with said heavy reiiuX condensate, directing said fraction comprising' gasoline constituents to a single pass reforming zone wherein the gasoline constituents are subiected to cracking temperature adequate to effect reforming into constituents of increased antiknock value, directing resultant reformed products into a second separating Zone wherein separation of residue from vapors takes place, passing said separated vapors into a second fractionating zone, introducing into said second l0. In the cracking of hydrocarbon oils, the process which comprisesv introducing a petroleum residual stock. into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a first separating zone wherein separation of vapors from liquid residue takes place, passing separated vapors into a first fractionating zone whereinthe vapors are subjected to fractionation to form a heavy reflux condensate, passing said heavy reflux condensate to a second cracking Zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect the formation of a further yield of intermediate constituents adapted to conversion into gasoline, directing resultant cracked products from the second cracking zone into a second separating Zone wherein separation of vapors from liquid residue takes place, passing the resultant separated vapors to said first fractionating Zone so that said vapors are subjected to fractionation together with the vapors from said first separating Zone to form said heavy reflux condensate as aforesaid, withdrawing liquid residue from said first separating zone and subjecting it to vacuum distillation in a flashing zone held under sub-atmospheric pressure to form a heavy vacuum distillate and introducing said heavy vacuum distillate into said rst fractionating zone so that any portion of the vacuum distillate remaining unvaporized after contact with the vapors undergoing fractionation will be charged to said second cracking Zone with said heavy reflux condensate, subjecting vapors in the first fractionating zone to further fractionation to separate a fraction comprising gasoline constituents from intermediate constituents, directing said fraction comprising gasoline constituents to a single-pass reforming Zone wherein the gasoline constituents are subjected to cracking temperature adequate to effect reforming into constituents of increased anti-knock value, directing resultant reformed products into a separate high pressure separating zone wherein separation of vapors from liquid residue occurs, fractionating the resultant separated vapors in a second fractionating Zone to separate a light distillate from higher boiling constituents, combining higher boiling constituents thus obtained with intermediate constituents obtained from the rst fractionating zone and directing the mixture to a recycling cracking zone wherein the mixture is subjected to high cracking temperature under conditions to eiTect conversion into gasoline constituents of high anti-knock quality, directing the resultant cracked products into said high pressure separating zone, passing liquid residue from said high pressure separating Zone and from aforesaid second separating zone into a flashing zone and directing resultant flashed Vapors into said first fractionating zone.

11. In the cracking of hydrocarbon oils, the process which comprises introducing a petroleum residual stock into a primary cracking zone wherein the oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of intermediate constituents adapted for conversion into gasoline, directing the viscosity-broken products into a first separating zone wherein separation of vapors from liquid residue takes place, passing resultant separated vapors into a rst fractionating"zone and subjecting the vapors therein to fractionation to separate as condensate heavy constituents from vapors and subjecting the latter vapors to further fractionation to form a lighter condensate, withdrawing liquid residue from said second separating zone and subjecting it to vacuum distillation in a ashing zone held under sub-atmospheric pressure, combining heavy constituents recovered from the vapors in the vacuum distillation with heavy constituents formed in said first fractionating Zone and passing the combined constituents to a second cracking zone wherein the mixture is subjected to cracking temperature under conditions to eiect the formation of a further yield of intermediate constituents adapted for conversion into gasoline, directing resultant cracked products from the second cracking Zone into a second separating zone, passing the resultant separated vapors into said rst fractionating zone, passing said lighter condensate to a separate cracking zone wherein the condensate is subjected to high cracking temperature under conditions to effect conversion into gasoline constituents of high anti-knock quality, directing the resultant cracked products into a high pressure separating zone wherein separation of vapors from residue takes place, fractionating separated vapors to form a desired light distillate, passing liquid residue from said high pressure separating Zone and from aforesaid second separating Zone into a flashing zone and directing resultant flashed vapors into said rst fractionating zone.

CHARLES W. NOFSINGER. DAVD T. SHAW.

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