US2745794A

US2745794A - Combination cracking process

Info

Publication number: US2745794A
Application number: US332392A
Authority: US
Inventors: Nicholas J G Alozery; William P Given
Original assignee: MW Kellogg Co
Current assignee: MW Kellogg Co
Priority date: 1953-01-21
Filing date: 1953-01-21
Publication date: 1956-05-15
Anticipated expiration: 1973-05-15

Description

May 15, 1956 I ALQZERY ET AL 2,745,794

COMBINATION CRACKING PROCESS Filed Jan. 21, 1955 4 Sheets-Sheet 1 94 ABSORBER CATALYTIC CRACKER FRACTIONATOR CRUDE THERMAL CRACKER COMBINATION FURNACE INVENTORS WILLIAM newer:

NICHOLAS J. G. ALOZERY FIG. I

ATTORNEYS y 1956 N. J. G. ALOZERY ET AL 2,745,794

COMBINATION CRACKING PROCESS Filed Jan. 21, 1955 4 Sheets-Sheet 2 F I G o I 5] 155 j 16} CRUDE FRACTIONATOR COMBINATION FURNACE Q 775 INVENTORS a 1]? WILLIAM P.G|VEN mug; 3 j! NICHOLAS J.G.ALOZERY OIL 1] 1 BY ATTOR NEYS May 15, 1956 J ALOZERY ET AL 2,745,794

COMBINATION CRACKING PROCESS Filed Jan. 21, 1955 4 Sheets-Sheet 4 6] f 22;; F e, 4 .128

CATALYTIC CRACKER INVENTORS WILLIAM P.G|VEN 2.98 29.9 303 NICHOLAS J. c. ALOZERY 50! 304 ATTOR NEYS United States Patent COMBINATION CRACKING PROCESS Nicholas J. G. Alozery, New York, and William P. Given,

Levittown, N. Y., assignors to The M. W. Kellogg Company, Jersey City,.N. 1., a corporation of Delaware Application January 21, 1953, Serial No. 332,392

11 Claims. (Cl. 196-49) This invention is a petroleum refining process which begins with the fractional distillation of crude petroleum into reduced crude, heavy gas oil, and light straight run products, and then follows this fractionation with an integrated combination of catalytic cracking, thermal cracking, and coking to convert the reduced crude and ing processes are separated (in suitable fractional distillation zones) into rich gas, unstabilized gasoline, and other fractions. The rich gas from all three cracking steps is passed through a common absorber in which gaseous hydrocarbons are absorbed by a common absorber stream derived from at least one of the cracking efliuents, the rich absorber oil is then combined with at least one of the cracking efliuents. In each of the three cracking processes, it is customary to fractionate the efliuent into a gasoline-containing distillate fraction and heavier fractions; but in the present combination process, it is a unique feature that the three eflluent fractions are continuously in equilibrium with each other by virtue of gas oil streams which continuously flow between them without intermediate storage or wastage of heat or pressure head. Indeed, in one preferred species, the coker vapor efliuent, the thermal cracking eflluent, and a gas oil stream from the fractionation of catalytic cracking eflluent all find their way into a single combination distillation tower. preferred species, a gas oil fraction (mostly heavy coker gas oil) from the combination tower is mixed with reduced crude on its way from the crude fractionation to coking.

Although petroleum refining was at first merely a fractional distillation of the crude oil into' a number of fractions, referred to as straight run products, modern demands for gasoline have resulted in the development of cracking processes for converting heavier petroleum components into gasoline. Each of the three cracking processes has its unique advantages and each complements the other two. Catalytic cracking is the blandest of the three; it is ideal for converting virgin gas oil to high yields of high octane gasoline. Thermal cracking is harsher and is not capable of doing with virgin feed what catalytic cracking does, but it has its best function in converting light cracked oils to gasoline. Thermal cracking produces lower octane but it is cheaper than catalytic cracking when employed with a feed which has been reduced by cracking to heavier hydrocarbons. Coking can be employed for a petroleum charge which is too heavy for either of the other two to digest efliciently. Coking is In a sub-species of the aforementioned 2,745,794 Patented May 15, 1956 adapted to the production of coke and coker hydrocarbon vapors; thermal and catalytic cracking are not satisfactory if coke production is high. Economic refining requires the employment of all three processes. In refineries of large capacity, for example 50,000 barrels per stream day or larger, satisfactory efliciency can be achieved with independent units; but in small refineries, provision for all these processes must be made with much lower. capitalization and lower operating costs. Applicants process is useful in a refinery of any size, but its advantages become particularly great in small refineries because it eliminates duplicate equipment and storage tanks; and it reduces operating costs because of savings in heat, pressure head, and maintenance costs. 7

Whatever the size of the refinery, however, the present process reduces the ground area occupied by uncombined units, the number of instrumentation centers, and the operating personnel.

Moreover, the component processes themselves are altered in character because the continuous flow of rich oil from the common absorber tower makes it possible to continuously and instantly shift light hydrocarbons from catalytic cracking efliuent to thermal gasoline as desired. The composition of the heavy gas oil which is returned to the coke drums is not the same in the present combination process as in the coking process, because it contains some constituents derived from thermal cracking eflluent, and even some derived from the catalytic crack ing eflluent by way of the absorber oil.

The behavior of the process is different by virtue of the absence of intermediate storage. Stored gas oil absorbs oxygen; when the oil is reheated for reintroduction into the process, some oxidation and deposition of clogging material takes place. Because of the continuing nature of the process, certain adjustments make themselves felt automatically. For example, the incoming crude passes in indirect heat exchange with reflux streams for the combination tower. When charge rate of the crude oil is increased or decreased, the various reflux streams are automatically cooled proportionately more or less. The absorber oil functions both as gas carrier and as relatively cool reflux; as it increases in flow to the combination fractional distillation tower, it simultaneously increases the gas content of that tower, increases the need for reflux, and itself provides the increased flow Other advantages of the invention may be understood after an explanation of the two specific embodiments which'are shown by flow diagrams in the accompanying four sheets of drawings, in which:

Figure 1 is a flow sheet diagram of a combination refinery in which coker vapors and thermal cracking eflluent are fractionated in separate fractional distillation towers; and

Figures 2, 3 and 4 represent a single flow sheet beginpressure of preferably between 0 and 500 p. s. i. g. If

the crude contains undesirable salts, such as magnesium chloride or calcium chloride, then it may be desalted in desalter 13, which may be of any conventional type, for

example, mixing with water caustic and electrostatically precipitating salts. The desalted crude is preferably preheated by heat exchange with reflux streams and then passes through crude coils 14 in combination furnace 15 and is heated to crude distillation temperatures of between 600 F. and 800 F. The crude enters crude fracionatnr .16 .at the inlet 17 near the lower .end. Reduced crude is withdrawn from the bottom of crude fractionator 16 through line 18, pumped by means of pump 19 through reduced crude coils 20 in combination furnace 15, whereby the reduced crude is heated to coking temperatures between 800 F .and 1000 F., and continuously fed to the coking step through line 21. Various light straight run fractions of successively lower boiling range may be withdrawn from crude fractionator 16 at successively higher elevations, for example, diesel oil through line 22, kerosene through line 23 and a petroleum solvent through linel l. .Each of these fractions is withdrawn from fractionator 16 and steam stripped in

steam strippers

25, 26 and 27, vapors being returned to the fractionator 16. The diesel oil is subsequently neutralized by washing with an aqueous alkali solution in caustic washer 28. The kerosene is converted to treated kerosene by being heated to 600 F. to 800 F. in furnace 29 at a pressure of about SD-p. s. -i. g., contacted with bauxite in bauxite contacting drum 30, fractionated in rerun tower 31, and passed to sulphuric acid treatment 32, and caustic wash 33. In rerun tower :31, the kerosene is ridded of light vapors and heavyoils.

The solvent fraction may be pumped through a caustic washer34 and a copper chloride contact tower 35, which serves ;to sweeten, 'i. e. convert mercaptan sulfur compounds toless odorous disulfides; a treated solvent is withdrawn at 36. Of course, the number of straight run products may be increased or reduced as economics dictate. For example, the diesel oil might be employed in part as catalytic cracking feed.

A gas oil fraction, the heaviest fraction next to the reduced crude withdrawn at 18, is withdrawn from the Lower part of the crude fractionator 16 through line 37 for catalytic cracking.

Straight run gasoline is withdrawn as a light gaseous fraction from the upper end of the crude fractionator 16 at line 38. Of course, a heavy straight run gasoline might be withdrawn from crude fractionator 16 as a liquid. The light straight run gasoline is partially condensed by means of condenser 39, and separated in drum 40. Vapors are withdrawn through 41 and are combined with rich gas flowing to .the absorber as will be explained hereinafter. The condensate is pumped by pump 42 into stripping tower .43 in which the light straight run gasoline is stripped by its .own vapor reboiled by means of reboiling circuit 44. Light straight run gasoline, or light straight run naphtha, is withdrawn through line 45 and treated to caustic washing and copper chloride contacting (as shown in Figure 2) to produce a treated light straight run gasoline.

Rich gas leaves the upper end of stripper 43 through line 46 "for subsequent combination with rich gas from coking, thermal cracking, and catalytic cracking.

fIn the lower part of Figure 1, the hot reduced crude (line 21) and the gas oil (line 37) from crude fractionator 16 are cracked in a continuous integrated system to produce coker gasoline (in coke drums 47), thermal gasoline '(in thermal cracking furnace 48) and catalytic gasoline (in cracker 49); rich gas is obtained as a remainder fromeach. of these cracking processes, and all the rich gases from the system, those derived from the three cracking processes and that derived by separation and stripping of the straight run gasoline are then passed through a single absorber 50.

The coke drums 47 are operated in alternate periods of coking and coke removal in the conventional manner. Hot reduced crude is diverted from line 21 into each of the drums 47 .during alternate periods by means of the valve system indicated generally by the numeral 51. Coke is removed from these drums by conventional coke drills or hydraulic cutters, indicated diagrammatically by numeral 52. Coker hydrocarbon vapors are removed throughline 53 and introduced into the lower end of 4 a coker effluent fractionating tower 54. Coke drums 47 are also provided with a circuit for handling steam and hydrocarbon vapors produced when the coke is steamed out following a charging period. This circuit is comprised of a cooler 55, separator drum 56, and a pump 57, all of which serves the purpose of returning oil to the coker efliuent fractionator 54. The blow-down stack 58 is also provided for the purpose of water scrubbing uncondensed vapors from drum 56. A light gaseous fraction is withdrawn from coker effluent tower 54. This gaseous fraction is comprised mostly of coker gasoline and it is necessary to separate it into a liquid distillate containing most of the coker gasoline, and a rich gas for diversion to absorber 50. Ordinarily, tower 54 may be operated at a pressure of 15 p. s. i. g. to 100 p. s. i. g. The coker hydrocarbon vapors may be passed through a valve 59, condenser 60, and into a drum 61, from which coker gasoline distillate may be withdrawn at 62. The rich gas from drum 61 leaves it by way of line 63 for compression in multistage compressor 64 up to the relatively high pressures of between 125 p. s. i. g. and 250 p. s. i. g., at which absorber is operated.

Coker efliuent fractionating tower 54 may be suitably refluxed at various elevations by withdrawing liquid, pumping it to a slightly higher pressure, cooling it, and returning it to the tower 54. Such combinations are indicated generally at 65, 66 and .67.

A part of the gas oil reflux withdrawn through line 67 is diverted to catalytic cracking by way of line 68 and catalytic cracking efiiuent fractionating tower 69. The most important intermediate stream of gas oil from coker efliuent gas tower 54, however, is that withdrawn at v70, pumped by pump 71 through line 72 to an intermediate point 73 in thermal efiiuent fractionating tower 74. A heavy fraction is withdrawn from the bottom of coker efiluent tower 54 through line 75 and recycled through pump 19, combination furnace 14 and line 21 to coke drums 47. However, instead of recycling all of this material, part or all may be diverted to catalytic cracker 49 V or withdrawn from the system at this point as fuel oil product.

A gas oil stream is continuously withdrawn from thermal cracking efiiuent fractionating tower 74 and pumped by pump 76 through line 77 to thermal cracking furnace 48. The hot thermal cracking effluent returns to tower 74 from furnace 48 by way of line 78. Tower 74 may also be supplied with a rich gas oil from absorber 50 by way of line 79 and 80. Reflux circuits 81 and 82 are provided for the upper and lower regions of tower 74.

A tar fraction is withdrawn from the bottom of tower 74 by way of line 83 and pump '84. This tar may either be withdrawn as product or returned to coke drums 47 by way of line 85.

Thermally cracked gasoline is withdrawn as a vapor from the top of tower 74 by way of line '86 and joins the rich gas from the straight run gasoline in line 46. The vapor is partially condensed in condenser 87 and separated in drum 88 into thermal gasoline condensate, which is withdrawn at 89, and rich gas which is passed to an intermediate stage of multistage compressor 64 by way of line 90.

The catalytic cracker is supplied with fresh feed in the form of gas-oil from crude fractionator 16 by way of line 37 which may conveniently 'join slurry oil withdrawn from the bottom of catalytic cracking efiluent 'fractionator' 69 at 91 and be pumped by pump 92 into catalytic cracker 49. Eifluent from catalytic cracker 49 is introduced into the bottom of catalytic cracking efiiuent fractionator tower 69 via line 93. A vapor, comprised mostly of catalytic gasoline, is withdrawn overhead from tower 69 through line 94, partially condensed in condenser 95 and separated in drum 96 into rich gas and unstabilized catalytic gasoline. The former is passed to compressor 64 by way of line 97 and the latter is pumped by pump 98 and line 99 to be mixed with compressed rich gas in line separator drum 102. The catalytic gasoline is stabilized in depropanizer 103 and debutanizer 104, both of which are provided with conventional reflux circuits 103a and 104a at the top and reboiler circuits 10312 and 104!) at the bottom. The unstabilized gasoline moves from drum 102 by way of pump 105, and from tower 103 to 104 by way of line 106. It is caustically washed and withdrawn as a product at 107. Lean light gas oil for absorber is obtained from catalytic cracking efliuent fractionating tower 69 at 108, being steam stripped in steam stripper 108a, and transferred to absorber 50 by way of line 109 and pump 109a.

The combination refinery of Figs. 2, 3, and 4 employs a single combination tower (seen in Fig. 3) in place of coker effluent fractionating tower 54 (of Fig. l) and thermal cracking etfluent fractionating tower 74 of Fig. 1.

Crude petroleum enters the system at 110 and is pumped by means of pump 111 through a heat exchanger 112, in which the crude petroleum is raised to a temperature of about 125 F., by indirect heat exchange with exhaust steam; the crude oil is next passed through a heat exchanger 113 through which it is heated to a temperature of about 220 F., by indirect heat exchange with reflux oil withdrawn from the top of the combination tower, as will be described hereinafter. The heated stream of crude oil flows through line 114 picking up an aqueous alkali solution of sodium hydroxide at 115 and water at 116, and then enters desalting drum 117, in which settling takes place; salt solution is withdrawn from desalting settling drum 117 at 118, and dry desalted crude is withdrawn overhead through line 119, passed through surge drum 120, and pumped by pump 121 through heat exchanger 122, in which the crude is heated from a temperature of about 220 F., to a temperature of about 540 F. by indirect heat exchange with hot reflux streams from intermediate points of the combination tower as will be described hereinafter. The hot crude next flows via line 123 through crude heater lines in combination furnace 124, being heated to a temperature of about 725 F., and flows via line 125 to a flash zone in the lower portion of topping tower 126, also designated as the crude fractionator. feet in vertical extent, provided with about 33 trays, and controlled to provide a temperature gradient ranging from about 710 F. near the bottom to about 235 F. near the top. From the standpoint of steps in the combination process, the two most important streams withdrawn from crude fractionator 126 are the reduced crude stream withdrawn from the bottom by way of line 127 and the gas oil stream for catalytic cracking withdrawn a short distance above the flash zone through line 128. The reduced crude stream flows into a surge drum 129 in which it mixes with heavy gas oil from the combination tower, as will be described hereinafter. The mixture of reduced crude and heavy gas oil is pumped by means of pump 130 and line 131 through coking heater lines in combination furnace 124 and then by way of line 132 to the coke drums as will be described hereinafter. In addition to the reduced crude streams and the gas oil streams from crude fractionator 126, straight run products are withdrawn at successively higher elevations and light straight run gasoline is withdrawn as a vapor from the top.

Relatively heavy straight run sidestream withdrawn at 133 may be stripped in 134, vapors being returned via' 135, and the stripped sidestream being pumped by way of pump 136 through cooler 137 to a caustic washer 138. This sidestream may be diesel oil, and may be subjected to subsequent conventional treatment, if desired. A part of the diesel oil side stream withdrawn at line 133 is pumped back to fractionator 126 by means of pump 139 being passed in heat exchange on the way through re- The crude fractionator is typically about 95 boiler 140. The reintroduced stream serves as supplemental reflux in the lower section of the tower. Because of the withdrawal of several side streams further up,'it would otherwise be necessary to reflux excessively in the upper part of the tower and greatly enlarge the upper part of the tower, in order to maintain adequate reflux in the lower section. Preferably, the refluxed stream enters crude fractionator 126 through line 141 at a point one or two trays above its point of withdrawal.

The next lighter sidestream is withdrawn a little ways farther up fractionator 126 at 142, stripped as before at 143, pumped and cooled at 144 and 145; this may be a kerosene stream suitable for finishing as a kerosene product.

Various other straight run streams may be withdrawn. In this example, the next higher stream, withdrawn at 146, stripped at 147, pumped by pump 148 through cooler 149 and caustic washer 150, may be heavy straight run gasoline suitable for conventional treating and blending.

Light straight run gasoline is withdrawn as vapor at the top of fractionator 126 through line 151, partially condensed in condenser 152, passed to reflux accumulator 153, and pumped by pump 154 in part back to fractionator 126 as reflux; the net production is diverted through line 155 to light straight run stripper 156 in which the light straight run gasoline is stripped by its own vapors, provided by heating a stream withdrawn through line 157, partially vaporized in previously mentioned reboiler 140. The stripped light straight run gasoline is withdrawn from the bottom of stripper 156, cooled at 158, caustic washed at 159, and is withdrawn from the combination circuit as light straight run gasoline product; or at least as light straight run gasoline suitable for such product finishing as may be desired.

Hydrocarbon vapors are withdrawn from the upper end of stripper 156 by way of line 160 at a temperature of about 143 F. and a pressure of about 60 lbs. per square inch. Usually these hydrocarbons will be butane and lighter, i. e., of lighter boiling point; however, the gasoline fraction may be increased or reduced, depending upon the light straight run gasoline specifications, by varying the stripping temperature and/or pressure.

Extra piping circuits are provided so that the kerosene and/or diesel products may be reduced by diverting a part of either or both of these streams to catalytic cracking or to the combination tower for thermal cracking, thus maximizing gasoline production and minimizing kerosene and diesel production. Various reasons dictate such manipulation of the refinery, for example, product specifications, the nature of the crude, the state of storage capacity, etc. Line 161 is employed for diverting kerosene or diesel oil streams, or both to catalytic cracking.

Line 162 is used for diverting kerosene or diesel oil streams or both to the combination tower.

Rich gas remaining uncondensed in reflux accumulator 153 is withdrawn through line 163 at relatively lower pressure, probably about 4 p. s. i. g., and like the stripped gas in line 160, eventually finds its way to a common compressor and absorber stream which will be discussed hereinafter.

Fig. 3 illustrates the coking and the thermal cracking sections of the combination refinery. The heated mixture of reduced crude and heavy coker gas oil, having been heated in combination furnace 124 to a temperature of about 930 F., is introduced during alternate periods of time into one or the other of paired coke drums indicated by the numeral 164. The hot oil is partially converted to coke in coke drums 164. During alternate periods of about 24 hours, solid coke is removed from the bottom of the coke drums 164. During charging periods, coker vapors are continuously withdrawn overhead through line 165 at a temperature of about 830 F. and at a pressure of about 80 p. s. i. g. and introduced into the lower end of a combination tower 166. Immediately after the charging period for each coke drum, the drum is purged with steam. The steam and purged vapors may be discharged into combination tower 166; but if desired, the

purging vapor mixture may be withdrawn through line 167, cooler 168, blow down accumulator drum 169, whereby the condensed portion is separated and the hydrocarbons returned via line 170, pump 171, and line 172 to an intermediate point in the lower section of the combination tower 166. Vapors from blowdown accumulator 169 are water scrubbed in blowdown stack 173; a water draw-off 174 is provided on accumulator 169.

The thermal cracking is carried out by continuously pumping, by means of pump 175, a stream of light gas Oil from an intermediate trap pan in combination tower 166 and passing it by way of line 176 to a thermal cracking furnace 177, in which it is heated to a temperature of about 985 F., before return to a low point in combination tower 166, through line 178. The pressure within combination tower 166 is typically or p. s. i. g., with S or 10 pounds pressure gradient from bottom to top. Pump increases the pressure on the thermal cracking feed oil to a suitable thermal cracking pressure of about 1000 p. s. i. g. at the thermal cracking furnace inlet. The hot eflluent leaves the thermal cracking furnace 177 at a pressure of about 720 p. s. i. g. In order to avoid coking in returning line 178, relatively cool light gas oil, obtained in a manner to be described hereinafter, is introduced by line 179 at pressure reduction valve 180, so that thermal cracking efliuent is reduced in'temperature to about 800 F. by direct heat exchange at the same time its pressure is reduced to about that in the lower part of combination tower 166.

Tar is pumped from the bottom of combination tower 166 by means of pump 181, cooled, and recirculated by a recirculation circuit 182, the net tar production being withdrawn at 183. However, if it is desired to further minimize tar production and maximize gasoline production, a substantial portion or all of the tar may be returned to coke drums 164 by way of recycle line 184. The tar may be steam stripped just prior to withdrawal by means of steam stripper 185.

A light gasoline fraction, comprised mostly of thermal and coker gasoline is withdrawn from the top of combination tower 166 at line 185, partially condensed in condenser 186 and separated in gas separator 187 into a rich gas withdrawn at 188 and unfinished gasoline prodnot at 189. The composition of both the rich gas in 188 and the gasoline withdrawn from 189 is affected by cornmingling of rich gas diverted from the straight run gasoline to line by way of line 160. The combination of straight run gasoline rich gas with the vapor fraction from combination tower 166 makes unnecessary any separate provision for cooling or processing the rich gas from the light straight run gasoline.

Reflux for the top of combination tower 166 is provided by Withdrawing liquid through line 190, cooling in heat exchanger 191 by indirect heat exchange with the crude charge, for example heat exchanger 113, seen in Fig.- 2. The reflux is further cooled in coiler 192 and pumped back into combination tower 166 by pump 193.

The mixture of thermal and coker gasoline (enriched to some degree by components of rich gas, may be light straight run gasoline) withdrawn from gas separator 187 by way of'line 189 is pumped by pump 194 via line 195 toa conventional gasoline stabilizing tower 196, whose reboiler 197 is heated by indirect heat exchange with a refluxing stream to be described hereinafter. Stabilized gasoline is Withdrawn from stabilizing tower 196 at 198, cooled in heat exchanger 199 by indirect heat exchange with the gasoline stream in line 195, further cooled by cooler 200, and caustic washed in caustic washing circuit 201. Stabilized and washed gasoline is withdrawn at 202 as a product or for further treatment. Overhead vapors are withdrawn through line 203, and partially condensed in condenser 204, condensate being returned to stabilizing tower 196 as reflux by means of pump 205 and vapors being withdrawn from reflux accumulator 206 by way of line 207 for use as fuel gas.

- certain important differences, however.

At an intermediate point in combination tower 166, third and fourth charge streams, supplementing coking efliuent and thermal cracking eflluent are introduced. One of these streams is surplus kerosene or diesel oil brought in through line 162 as previously described and introduced into tower 166 through line 208, or in exceptional cases through line 209. The fourth source of charge for combination tower 166 is a stream of rich oil derived from an absorber to be described hereinafter and containing components of rich gas from straight run gasoline, from coking and thermal cracking, and from a catalytic cracking step yet to be described. This rich gas is brought in via line 210. The continuous flow of rich oil from the absorber to the upper part of combination tower 166 thusprovides a common meeting place for products of every step in the combination process. It is a novel characteristic of the invention that at least part of the feed of combination tower 166 (or, if there are 2 towers, to the thermal carcking efliuent fractionator) is a light gas oil, usually a rich oil of the nature already described, or lean oil derived from the efliuent of catalytic cracking.

Combination tower 166 is refluxed at various elevations with light gas oil withdrawn at line 211, cooled as previously described in reboiler 197, returned by way of line 212 to heat exchanger 213 by indirect heat exchange with crude flowing through heat exchanger 122 in Fig. 2. The light gas oil reflux is further cooled in cooler 214 then pumped via pump 215 and

lines

216 and 217 to various intermediate elevations in combination tower 166.

Heavy gas oil is withdrawn from the lower section of combination tower 166 by way of line 218. Part of this is cooled in heat exchanger 219, preferably by indirect heat exchange by crude as in the case of heat exchanger 213 and then pumped by pump 220 back to combination tower 166 by way of line 221. A second portion of the withdrawn heavy gas oil is diverted at A to surge drum 129 in Fig. 2, as previously described. Vapors from surge drum 129 return as indicated in A by way of line 222 to combination tower 166.

If desired, the combination tower may be employed as a source for part or all of the lean oil required in the absorption step. A suitable place for diverting gas oil to be used in this fashion is by way of valve 223 and line 224 immediately downstream from heat exchanger 213.

Combination tower 166 performs the function of both coker gas fractionator 54 and thermal cracking effluent fractionator 74 in the embodiment of Fig. 1. There are Whereas in the embodiment of Fig. 1 heavy coker gas oil was withdrawn from an intermediate point in the coker gas fractionator 54 and diverted by way of line 68 to catalytic cracking efliuent fractionator 69 whereby the heavy coker gas oil becomes part of the feed to the catalytic cracking step, in the combination tower version, the heavy gas oil stream withdrawn from combination tower 166 by way of line 218 finds its way back to the coke drums in the manner already described. Although the heavy gas oil withdrawn through line 218 contains substantially all of the heavy coker gas oil, it also contains a heavy component of the thermal cracking efliuent. Other differences between the two embodiments illustrated follow from the fact that all the vapors from both the coker gas eflluent and the thermal cracking effluent are mixed within the same fractional distillation zone and are withdrawn at a temperature somewhat higher than would be necessary to operate the coker gas efliuent fractionator 54. Combination tower 166 operates at a typical pressure of about 65 p. s. i. g., but the pressure may range from between 20 to 350 p. s. i. g. depending on economic and process conditions at the time of design. At pressures of 60 to 70 p. s. i. g., a typical temperature range within combination tower 166 would be from about 780 F. at the bottom to about 340 F. at the top. However, at higher pressures these temperatures would be correspondingly higher; but whatever the pressure, the practical temperature ranges for the bottom and top respectively would be about 100 F. to 450 F. and 600 F. to 900 F. A satisfactory gradient of temperature is continuously maintained by the rate of reflux at the difierent points already described. The primary object is to so regulate conditions within combination tower 166 as to fractionate satisfactorily, in the order of decreasing boiling range, tar, a heavy gas oil for further coking and for refluxing, a light gas oil for thermal cracking and for refluxing and a vapor fraction comprised of gasoline and lighter ends.

Combination tower 166 provides a convenient means for shifting cracking load back and forth between coke drums and thermal cracker so as to operate both at maximum load etficiency. The temperatures at the top of combination tower 166 are determined by the specifications laid down for the gasoline to be withdrawn there. The temperatures at the bottom of the combination tower are established by tar specifications. But at the elevations of the side streams (light gas oil for thermal charge and heavy gas oil for recycle to coker) Withdrawn through

lines

218 and 175, the operator may manipulate temperatures so as to increase or reduce the flow of either of the streams, this manipulation being accomplished by increasing or decreasing the rate of reflux just above these points of withdrawal.

The rich gas separated from the overhead gasoline fraction through line 188 is passed through a drum 225 to entrap any uncondensed liquid and then by way of line 226 to an intermediate stage of a multistage compressor 227 (Fig. 4).

The principal source of fresh feed for catalytic cracking is the gas oil stream withdrawn from crude fractionator 126 through line 128. Most of the time this stream will flow directly into catalytic cracker 228. Catalytic cracker 228 is comprised of a reactor section 229, superimposed on a regenerator section 230, each containing its own fluidized bed of catalyst, not shown. Catalyst is continuously circulating from reactor 229 to regenerator 230 by way of steam stripper 231 and standpipe 232; regenerated catalyst and catalytic cracking feed enter reactor 229 through catalyst riser 233. Air is supplied to regenerator 230 at 234 and flue gas escapes by way of cyclone 235 and stack 236. Catalytic cracking effluent is withdrawn by way of cyclone separator 237 and line 238 to the bottom of a catalytic cracking eflluent fractionator 239, in which said efliuent is fractionated into slurry oil withdrawn at the bottom of fractionator 239 through line 240, and vaporous hydrocarbons comprised of catalytic gasoline and lighter components withdrawn at the top, through line 241.

The vapor fraction of the catalytic cracking efliuent is partially condensed by means of condenser 242, condensate is separated from vapor in gas separator 243, the condensate being pumped up to a pressure of about 135 p. s. i. g. by means of pump 244 and the remaining vapor being passed through drum 245 to eliminate liquid and then by way of line 246 to multistage compressor 227, in which it is compressed up to a pressure of about 135 p. s. i. g. At an intermediate stage it is commingled with rich gas from line 226 (separated from the thermal and coking gasoline taken overhead from combination tower 166). The compressed rich gas is withdrawn from compressor 227 by way of line 247, combined with the pumped condensate from line 248, passed through cooler 249 to a high pressure gas separator 250.

The condensate in high pressure gas separator drum 250 is an unstabilized catalytic gasoline. This gasoline is continuously withdrawn through line 251, heated in heat exchanger 252 (by indirect heat exchange with depropanized gasoline), and passed by way of line 253 to depropanizer tower 254, and is provided at its upper end with a reflux circuit 255 and a reflux discharge 256' and at the lower end with a reboiler circuit 257. De-

10 propanized gasoline leaves the bottom of depropniZr tower 254 through line 258, is cooled in heat exchanger 252, and enters debutanizer tower 259 by way of line 260. Debutanizer tower 259 is provided with a reflux circuit 261 at its upper end and a tap 262 for withdrawing net butane production, a'reboiler 263 is employed for introducing heat in the lower region of debutanizer tower 259. Debutanized gasoline is withdrawn from the bottom of debutanizer tower 259 through line 264, cooled in cooler 265, caustic washed in caustic washer 266 and withdrawn at 267 as catalytic gasoline product.

Reboilers

257 and 263 may conveniently derive their heat by indirect heat exchange with a stream of slurry oil from the bottom of catalytic effluent fractionator 239, the slurry oil being brought to the reboilers by way of line 268 and returned to the catalytic cracking etiluent fractionating system by way of line 269.

Compressed rich gas derived from all the gasoline streams produced by the combination unit is withdrawn from high pressure gas separator 250 through line 270 and introduced into the bottom of an absorber tower 271, in which it is counter-currently contacted with a downflowing light gas oil in order to absorb light hydrocarbons into a gas oil. light gas oil is generally derived as a side stream of the catalytic cracking eflluent fractionator 239; but all or a part of the light gas oil for the absorber tower 271 may be obtained from combination tower 166, for example through line 224 by manipulation of the valve 272. The preferred arrangement, however, is to withdraw a stream of light gas oil from catalytic cracking efiiuent fractionator 239 through line 273, passing it through steam stripper 274, and pumping it by means of pump 275 through line 276, cooling it by means of heat exchanger 277 and cooler 278 before pumping it by means of pump 279 into the top of absorber tower 271. The light gas oil entering the top of the absorber tower 271 is conventionally referred to as lean oil, and as rich oil as it leaves the bottom of absorber tower 271 by way of line 280, because it has absorbed a substantial percentage of propane and heavier hydrocarbon vapor from the rich gas as said gas ascends through the tower. Conversely, the rich gas entering at line 270 leaves the top of absorber 271 through line 281 as lean gas suitable for fuel gas.

Catalytic cracking efliuent fractionator 239 may be suitably refluxed by returning some of the overhead condensate from line 248 by way of line 282; reflm; for the mid-point may be obtained by diverting part of the lean light gas oil entering the top of absorber 271 and returning it to catalytic cracking efiluent fractionator 239 byway of line 283. The lower region of catalytic efliuent fractionator 239 may be refluxed by returning some of the slurry oil, preferably slightly cooled. The piping arrangement for slurry oil withdrawn through line 240 provides for pumping it by means of pump 284 directly to the charging valve 285 in the bottom of the catalytic cracker 228 by way of line 286. At least part of the slurry oil, sometimes all of it, flows directly to the catalytic cracker. A second part is continuously being returned to catalytic cracking efl'luent fractionator 239 as reflux by way of line 287, boiler 288 (in which the slurry oil is cooled and steam is generated), and then by

lines

289 and 290 to tower 239. As a temperature control feature, some of the slurry oil may be diverted through line 291 and line 292 to the catalytic cracking charge.

Excess kerosene or diesel oil diverted to catalytic cracking by way of line 261 may be heated in furnace 293 before continuing to catalytic charge via lines 292 and 286, and charge valve 285. As a control feature, unheated material from line 161 may be diverted to catalytic cracking feed by way of

lines

294 and 295.

Although all the heavy gas oil may be continuously introduced directly into catalytic cracking by way of line 128, all or a part of this fresh feed may be diverted ,through line 295 to line 296, and-then by way of line 11 290, to the lower region of catalytic cracking efiiuent fractionator 239, so that the fresh feed finds its way to the catalytic cracker 228 in a mixture with the slurry oil withdrawn at line 240. This would be done when there seemed to be inadequate downflowing liquid in fractionator 239 to wash down catalyst.

In a unit of the combination type herein described many savings have been effected by integrating all operations, eliminating duplicate pieces of equipment, eliminating storage capacity, saving heat and pressure head and making each product according to a specification which is continuously affected in most cases by the specifications of other products. However, in order to make it possible to temporarily shut down parts of the refinery for occasional emergencies, inspections, or repairs, 2 storage tanks are provided in which may be stored enough in process oil to keep most of the refinery running during shutdown of one component part. These storage tanks are the catalytic feed flywheel tank 297 and the termal feed flywheel tank 298. Catalyst feed flywheel tank 297 is filled during normal operations by way of lines 295 and 299, and cooler 300. When it is necessary to continue operation of the catalytic cracking section during shutdown of other sections of the refinery, catalytic feed is pumped through tank 297 by means of pump 301 and by way of

lines

299, 295 and 128 to catalytic cracking feed valve 285. Tank 298 is filled with feed suitable for combination tower 166 during normal operation by diverting to it a stream of gas oil through line 302 and cooler 303. During shutdown of the catalytic cracking section, for example, thermal feed may be pumped by means of pump 304 from tank 298 through line 305 to line 210 to combination tower 166.

It will be understood that if the market for coke is poor and the market for fuel oil is good, that it will be preferred to do less coking, or to eliminate coking almost entirely, by diverting the heated reduced crude. from furnace or furnance 124 around the coke drums (which would be out of use when operating in this manner) directly to fractionating tower 54 or combination tower 166, respectively. In this manner, the furnace ordinarily serving as a coker furnace actually functions as a vis-breaking furnace. The combination unit then functions as a balanced combination of vis-breaking, thermal cracking, and catalytic cracking instead of the combination of coking, thermal cracking, and catalytic cracking. A significant range of control of the relative productions of coke and fuel oil is possible by varying the amount of heavy gas oil from the combination tower recycled to the coker furnace, a reduction in recycle rate increasing the relative fuel production, and vice versa.

Additional advantages of my invention are illustrated in the following example. The reactants and their proportions, and other specific ingredients and conditions, are presented as being typical and should not be construed to limit the invention unduly. A Redwater crude of 34.9" A. P. I. was charged to the topping tower for several weeks and fractionated as follows:

TABLE A. S. T. M. Distil- Vol. perlation R ng cent on crude charge Fraction I. B. P.

Gas to Recovery Virgin Naphtha. Solvent Diesel Oil Unstrirriiled Virgin Heavy Gas Reduced Crude 12 Temperatures and pressures within the topping tower Operating pressure at flash zone p. s. i. g 9.0 Temperatures Base F 685 Flash zone F 710 'Virgin heavy gas oil drawofina F 600 Diesel oil drawoff F 455 Kerosene drawoif F 394 Solvent drawoff F 350 Fractionator top a F 235 The heavy gas oil fraction was withdrawn at a temperature of about 600 F. and pumped to a pressure of about p. s. i. g. and injected into a fluidized catalytic cracker wherein the heavy gas oil was cracked at a temperature of about 960 F. and a pressure of about 15 p. s. i. g., a catalyst to oil ratio (basis of total reactor charge) of about 4 to 1 and a liquid volume conversion of 66 .per cent (basis of fresh feed). The efiluent of the catalytic cracking zone and part of the absorber rich oil were charged to the catalytic cracking efiiuent fractionating tower. A certain amount of a slurry and heavy gas oil is recycled to the catalytic cracking. The combined charge of heavy virgin gas oil plus rich oil charged to the section comprising the catalytic reactor and the catalytic efiluent fractionating tower was approximately 2900 B. P. S. D. and produced yields which were about as follows on a weight per cent basis of this charge:

Weight percent Catalytic cracked gas and gasoline 37.0 Lean oil to absorber 57.5 Catalytic cracking-coke 5.5

Tower base F 507 Cycle oil drawofi F 448 Fractionator top F 264 The light gaseous fraction was cooled to condense about 60 weight per cent, and the uncondensed portion was compressed to a pressure of 55 p. s. i. g. in the first stage of the compressor system. The condensed portion was pumped to a pressure of about 160 p. s. i. g., recontacted with vapors from the second stage of the compressor and the total efiiuent was flashed at a pressure of about 137 p. s. i. g. and a temperature of about F. The uncondensed vapors (or rich gas) were charged to the absorber. The condensed portion was pumped to a pressure of about 310 p. s. i. g. and charged to the stabilizer.

The reduced crude from the bottom of the topping tower was mixed with heavy coker gas oil from the combination tower and the mixture was passed through a furnace and thence to coke drums to produce coke and coker vapors. The coker vapors at a temperature of approximately 830 F., part of the rich oil from the absorber, and thermal cracking efiiuent were then charged to a combination tower to produce fuel oil and thermal cracked gas plus gasoline which was destined for subsequent steps.

The combined total charge to the coking and thermal cracking section consisting of reduced crude and part of the absorber rich oil'which comprised the net production of catalytic cycle oil, was approximately 2100 B. P. S. D., and produced yields which were about as follows on a weight per cent basis of the charge:

Weight percent Gas plus gasolinem 57 Fuel oil 26 Coke 17 The thermal feed fraction from said combination tower was continuously passed through a thermal cracking furnace and thermally cracked at temperatures of 966 F. and pressures of 720 p. s. i. g. and the effiuent quenched oil from combination tower, and introduced into said combination fractionating zone at an intermediate point having a temperature of about 780 F.

The gasoline fraction from the upper end of the combination fractionating zone was cooled to a temperature of 100 F. to condense out a 70 weight per cent fraction of unstabilized gasoline. The uncondensed portion was then combined with the partially compressed uncondensed portion of the catalytic cracking effluent and further compressed to a pressure of 137 p. s. i. g. The condensed liquid was pumped to a similar pressure and mixed with the compressed vapor at a temperature of about 150 F. The mixture is then cooled to a temperature of about 100 F. and the high pressure liquid so formed was withdrawn as unstabilized gasoline having an A. S. T. M. end point of 400 F. The remaining rich gas is charged to the absorber. The rich absorber oil is then charged to the combination cracking zone.

A 60 weight per cent of said rich oil from the absorber was charged to the catalytic cracking effluent fractionation step.

The stabilized gasoline was then charged to a debutanizer tower which operated at a pressure of 80 p. s. i. g. An overhead liquid butane product was removed for vapor pressure blending purposes with the thermal and straight run gasolines. The debutanizer bottoms product was catalytic gasoline and was cooled and caustic washed.

The following yields were obtained when charging approximately 1200 B. P. S. D. of unstabilized separation liquid to the stabilizer and debutanizer section:

Charge:

Unstabilized gasoline to stabilizer.... percent 100 Yields:

Although this process has been described and exemplified in terms of its preferred modifications and the above example, it is understood that various changes may be made Without departing from the spirit and the scope of the disclosure and the claims. For example, as shown in the drawings and description, there may be either a single combination tower or two effluent fractionating towers in its stead. Moreover, a vacuum still might have been employed as follows:

Reduced crude from the crude fractionator (16 or 126) would be processed in a vacuum still to yield an overhead gas oil stream and a heavy residuum bottoms. The overhead gas oil would be charged to the catalytic cracker. The residuum bottoms would be processed in either of the following manners dependent on the refinery condition.

(a) Residuum bottoms would be charged to a heater and heated to coking temperatures and the effluent vapors would discharge to the combination tower.

(b) Residuum bottoms would be charged to a heater and subjected to a vis-breaking operation in which the viscosity of the vacuum residuum would be reduced to that of a marketable fuel oil. The vis-breaker gasoline and gas oil would then enter the thermal stream.

Herewith is presented a typical overall weight balance of all products from this refinery based on crude and 550 and 750 F. final.

It will be further understood that finely divided catalyst includes not only powdered catalyst but those of t the pellet type used in other types of catalytic cracking,

since the invention is not restricted to fluidized catalytic cracking, although the latter is the preferred form.

Each step of the process is characterized by a tolerable range. The crude petroleum may have been an A. P. I.-

gravity between about 10 and 50. The reduced crude may have an initial boiling point ranging between 350 F. and 850 F., the heavy gas oil fractions boiling ranges being between 300 and 700 F. initial, and 600 to 1000" F. final. Pressures and temperatures in the topping tower may vary from zero to 50 p. s. i. g. and temperatures of between 400 and 800 F. at the bottom.

The boiling points referred to in the foregoing specification and in the boiling points given hereafter, refer to the American Society for Testing Materials standard procedures.

The reduced crude fraction leaves the topping tower at a temperature of between 350 and 775 F. and is heated to coking temperatures of between 770 F. and 1000 F. to enter the coke drums, producing coker hydrocarbon vapors having a final boiling of between 600 and 1100 F. These vapors are transferred from the coke drums to the coking efiiuent fractionation zone without cooling below a temperature of about 700 F. or being allowed to fall beneath the pressure of about 15 p. s. i. g. The vapors are fractionated at a pressure of between 15 and 200 p. s. i. g. and the product fractions always include a thermal cracking light gas oil fraction having a boiling range between 300 and 500 F. initial This thermal cracking feed fraction is withdrawn from the fractional distillation zone at a temperature of 600 to 800 F. and a pressure of 20 to 200 p. s. i. g. Thermal cracking conditions may be in a range of between 900 and 1100 F., under a pressure of 50 to 1000 p. s. i. g. The thermal cracking efiiuent is quenched to a temperature of between 900 and 700 F. The two gasoline-containing efliuent fractions from the catalytic cracking fractionation zone and from either the combination fractionating zone or the coking effluent fractionation zone and the thermal cracking efiiuent fractionation zone, are cooled to a temperature of between and F. to condense unstabilized gasoline fractions, the uncondensed portions being compressed to absorber pressure which may be between 50 and 350 p. s. i. g.; the remaining unstabilized gasoline will have an A. S. T. M. end point of between 350 to 450 F. The absorber oil may be a lean gas oil side stream from the catalytic cracking efiiuent fractionation zone having an A. S. T. M. boiling range of between 350 to 500 F. initial and 600 to 700 F. final boiling point.

We claim:

1. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having a boiling range starting between 400 F. and 900 F., a heavy gas oil fraction having a boiling range of between 300 F. to 700 F. initial and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said heavy gas oil from said crude petroleum distillation zone at a pressure between zero and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F. and catalytically cracking said oil; withdrawing an efliuent from said catalytic cracking step at a temperature of between 850 F. and 1000 F. and a pressure of between 5 and 50 p. s. i. g., and introducing said effluent into a vertically extended catalytic cracking efliuent fractionation zone operating at-a temperature of between 90 to 200 F. at the top and 600 to 900 F. at the bottom, and a pressure of between zero and 50 p. s. i. g., without reduction in temperature of said effluent below 600 F. before introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 to 450 F. from the upper end of said catalytic cracking effluent fractionation zone, cooling it to a temperature not higher than 120 F. to partially condense at least 40 per cent weight of said effiuent, compressing the uncondensed portion to an intermediate pressure of at least 25 p. s. i. g., pumping the condensed portion to a pressure of at least 125 p. s. i. g.; withdrawing said reduced crude from said crude petroleum fractionation step, heating it to coking temperatures of between 770 F. and 1000 F., and coking it to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and 1100 F.; flowing said coker hydrocarbon vapors to a vertically extended combination fractionation zone without lowering their temperature below 780 F. before introduction therein; fractionating said hydrocarbon vapors within said combination fractionating zone under a pressure of 15 to 350 p. s. i. g. to obtain several fractions, including a light gas oil fraction having a boiling range between 200 F. to 500 F. initial and 550 F. to 750 F. final; withdrawing said light gas oil fraction from said combination fractionating zone at a temperature of 500 F. to 800 F. and a pressure of 15 to 350 p. s. i. g., thermally cracking said thermal cracking feed fraction at final temperatures of between 900 F. and 1100 F.; introducing effluent from said thermal cracking into said combination fractionating zone; withdrawing from said combination fractionating zone a heavy gas oil having a boiling range between 450 F. and 650 F. initial and 700 F. and 1000 F. final, and recycling said heavy gas oil for further coking in said coking step; withdrawing a fraction composed primarily of gasoline from the upper end of said combination fractionating zone, cooling to a temperature less than 200 F. to partially condense said fraction into an unstabilized gasoline; combining the uncondensed portion of said fraction with said compressed uncondensed portion of said catalytic cracking efiluent and compressing the mixture to a pressure of between 125 and 350 p. s. i. g.; combining said compressed mixture with said condensed catalytic cracking efliuent at a pressure of between 125 and 350p. s. i. g. and a temperature of between 80 F. and 200 F., to produce a high pressure rich gas and a distillate liquid composed primarily of unstabilized gasoline having a final boiling point of 350 F. to 450 F.; forming a stream of lean light gas oil at least partly by withdrawing a stream having a boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said eflluent fractionation zones, counter-currently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavier hydrocarbons from said rich gas and thereby produce a lean gas and a rich oil; and returning said rich oil to at least one of said efiluent fractionation zones.

2. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling point between 400 F. and 900 F., a heavy gas oil fraction having a boiling range of between 300F. to 700 F. initial and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said heavy gas oil from said crude petroleum distillation zone at a pressure between and 50 p. s. i. g. and a temperature between about 500 F. and

and 800 F. and introducing said heavy gas oil into a fluidized mass of cracking catalyst without reducing the temperatures or pressure of said heavy gas oil below 450" F. and p. s. i. a. respectively and catalytically cracking said oil; withdrawing an effluent from said catalytic crackiru step at a temperature of between 850 and 1000 F. and a pressure of between 5 and 50 p. s. i. g., and introducing said'efiluent into a vertically extended catalytic cracking eflluentfractionation zone operating at a temperature of between to 200 F. at the top and 600 F. to 900 -F. at the bottom, and a pressure of between zero and 50 p. s. i. g. without reduction in temperature or pressure of said effluent below 600 F. and zero p. s. i. g. respectively; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking efiluent fractionation zone, cooling to a temperature of less than about 200 F. to partially condense at least 40 per cent weight of said eflluent, compressing the uncondensed portion to an intermediate pressure of at least 25 p. s. i. g., pumping the condensed portion to a pressure of at least p. s. i. g.; withdrawing said rereduced crude from said crudepetroleum fractionation step, heating it to coking temperatures of between 770 F. and 1000 F., and coking it to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and 1100 F.; introducing said coker hydrocarbon vapors into a vertically extended combination fractionation zone without falling below atemperature of 780 F. and a pressure of 15 p. s. i. g.; fractionating said hydrocarbon vapors within said combination fractionating zone under a pressure of 15 to. 250 p. s. i. g. to obtain several fractions, including a thermal cracking light gas oil feed fraction having a boiling range between 200 F. to 500 F.'initial and 550 F. to 750 F. final; withdrawing said thermal cracking feed fraction from said combination fractionating zone at a temperature of 600 F. to 800 F. and a pressure of 20 to 250 p. s. i. g., thermally cracking said thermal cracking feed fraction at final temperatures of between 900 F. and 1100 F., quenching said efiluent to a temperature of between 650 F. and 850 F. and introducing the liquefied efliuent into said combination fractionating zone; withdrawing from said combination fractionating zone a heavy gas oil having a boiling range between 450 F. and 650 F. initial and 700 F. and 1000 F. final, and recycling said heavy gas oil for further coking in said coking step; withdrawing a fraction composed primarily of gasoline from the upper end of said combination fractionating zone, cooling to a temperature of 80 F. to 200 F. to partially condense said fraction into an unstabilized gasoline; combining the uncondensed portion of said fraction with said compressed uncondensed portion of said catalytic cracking effluent and compressing the mixture to a pressure of between 125 and 350 p. s. i. g.; combining said compressed mixture with said condensed catalytic cracking efiluent at a pressure of between 125 and 350 p. s. i. g. and a temperature of between 80 F. and 200 F. to produce a high pressure rich gas and a high pressure distillate liquid composed primarily of unstabilized gasoline having a final boiling point of 250 F. to 450 F.; forming a stream of lean light gas oil by withdrawing a stream having a boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said effluent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavier hydrocarbons from said rich gas and thereby produce a lean gas and a rich oil; and returning said rich oil to at least one of said efiiuent fractionation zones.

3.'A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, season F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an eflluent from said catalytic cracking step at a temperature of between 850 Ffand 1000 F., and introducing said effluent into a verticallyextended catalytic cracking efduent fractionation zone operating at a temperature of between 90 F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said efiluent below 600 F. and 0 p. s. i. g., respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking efiluent fractionation zone, cooling to partially condense said effluent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation step, heating it to temperatures of between 770 F. and 1000 F., and coking any desired portion thereof to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and 1100 F., introducing the uncoked portion and coker to eflluent hydrocarbon vapors into a vertically extended combination fractionation zone; fractionating hydrocarbon vapors within said combination fractionation zone under a pressure of 15 to 350 p. s. i. g. to obtain several fractions, including a light gas oil fraction having a boiling range between about200 F. to 500 F. initial and about 550 F. to 750 F. final; withdrawing said light gas oil fraction from said combination fractionating zone, heating said light gas oil fraction to thermally crack it at final temperatures of between 900 F. and 1100 F.; introducing efiluent from said thermal cracking into said combination fractionation zone; withdrawing from said combination fractionation zone a heavy gas oil having a boiling range between 450 and 650 F. initial and 700 F. and 1000 F. final, and recycling said heavy gas oil to at least one of said heating steps; withdrawing a fraction composed primarily of gasoline from the upper end of said combination fractionating zone, cooling it to partially condense said fraction; forming a stream of rich gas derived at least in part from said uncondensed portions taken from said catalytic cracking efiiuent fractionation zone and said combination fractionation zone; forming a stream of lean light gas oil at least partly by withdrawing a stream having a boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said effluent fractionation zones; countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavier hydrocarbons from said rich gas and thereby produce a lean gas and a rich oil; and returning said rich oil to at least one of said effluent fractionation zones.

4. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between 0 and 5 0 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an efiluent from said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said efiluent into a vertically extended catalytic cracking efiluent fractionation zone operating at a temperature of between F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said effluent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking efiluent fractionation zone, cooling to partially condense-said eifluent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation step; heating it to temperatures in the coking and vis-breaking range; passing hydrocarbon fluids derived from said heated reduced crude to a second efiiuent fractionation'zone; fractionating said hydrocarbon fluid within said second eflluent fractionation zone to obtain several fractions; forming a thermal cracking gas oil feed fraction having a boiling range between 200 F. to 500 F. initial and 500 F. to 750 F. final, at least partlyfrom a gas oil sidestream withdrawn from one of said two previously mentioned effluent fractionation zones; thermally cracking said thermal cracking feed fraction at final temperatures of between 900 F. and 1100 F., quenching said efiluent, and introducing it into a thermal cracking efiluent fractionation zone; withdrawing overhead vapor fractions from said second efliuent fractionation zone and said thermal cracking efiluent fractionation zone, partially condensing them, and combining at least partof the uncondensed vapors remaining, with said uncondensed vapors from said catalytic cracking efiluent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said efiiuent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a rich gas and a rich .oil and returning said rich oil to at least one of said eflluent fractionation zones.

5. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone ata pressure between 0 and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an efiiuent from said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said efiluent into a vertically extended catalytic cracking effluent fractionation zone operating at a temperature of between 90 F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature of pressure of said efiiuent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking effluent fractionation zone,

1'9 cooling to partially condense said efliuent, compressing the uncondensed'portion and pumping'th'e condensed portion .to'higherpressure; withdrawing said reduced crude.

from said crude petroleum fractionation step; heating it to temperatures of between 770 F. and 1000 F. and

COkingat least part to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and 1100 F., introducing said coker hydrocarbon vapors into a coker efiluent fractionation zone without reduction in temperature of saidefiluent below 780 F; fractionating said coker efiluent within said coker effluent 'fractionating zone to obtain several fractions; forming a between900 F. and 1100 F., quenchingsaid efiiuent,

and introducing it into a thermal cracking efiiuent fractionation zone; withdrawing overhead vapor fractions from said coker efiluent fractionation zone and said thermal efiiuent fractionation zone; partially condensing 'them, and combining at least part of the uncondensed vapors remaining with said uncondensed vapors from said. catalytic cracking efiluent fractionation zone to make up at least part of a rich gas underpressure; forming a stream of lean light gas oil from a gas oil sidestream withdrawn from said catalytic cracking efiiuent frac tionation zone; countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a lean gas and a' rich oil; and returning at least part of said rich oil to said thermal cracking efiiuent fractionation zone.

6. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having 'an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between 0 and '50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy' gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an effluent from said catalytic cracking 'step at a temperature of between 850 F. and 1000 F., and introducing said efiiuent into a vertically extended catalytic cracking effluentfractionation zone operating at a temperature of between 90 F. and 200 'F. atthe top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said ,efiiuent below 600 F. and 0 p. s. i. g. respectively, prior to' said introduction withdrawing a light gaseous fraction having a boiling range ending at from 250 F; to 450 F. from the upper end of said catalytic cracking .eflluentfrac'tionation zone, cooling to partially condense said efliuent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said reduced crude from said crude'petroleum fractionation step; heating it to temperatures of between 770 F. and 1000 F. and coking at least part to produce coke and .cokerhydrocarbon vapors having a final boiling point between600 F. and

1100 F.; introducing said coker hydrocarbon vapors into a coker'eifluent fractionation zone without reduction in temperature of said effluent below .780" 'F.; fractionating said coker efiluent within said coker efiiuent fractionating zone to obtain several fractions; forming a thermal crack-v ing gas oil feed fraction having a boiling range between 200 F. to 500 F. initial and 500 F, to 750 F. final, at least partly from agas oil sidestream withdrawn from said catalytic cracking effiuent fractionation zone; thermally cracking. said thermal cracking feed fraction eat final temperatures. of between 900 F. and 1100 F., quenching said efiiuent, and introducing it into a thermal cracking effluent fractionation zone; withdrawing overdensed vapors from said catalytic cracking cflluent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by'withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling 7 point from at least one of said efiiuent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a rich gas and a rich oil; and returning said rich oil to at least one of said effluent fractionation zones.

7. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuous, ly introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F., to 700 F. initial, and

600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between 0 and 50 p. s. i. g. and a temperature between 500 F. and 800F. and contacting at least part 'of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F.', and catalytically cracking said oil; withdrawing an effluent from said catalyst cracking step at a temperature of between 850" F. and 1000 F., and introducting said effluent into a vertically extended cataytic cracking efliuent fractionation zone operating at a temperature of between F. and 200 F. at the top, and 600 F. to' 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said efliuent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking effluent, compressing the uncondensed portion and pumping'the condensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation step: heating'it to temperatures of between 770 F. and 1000 F. and coking at least part to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and l F.;-introducing cokerhydrocarbon vapors into a coker effluent fractionation zone without reductionin temperature of said effluent below 780 F.; fractionating said coker efiluent within said coker effluent fractionating zone to obtain several fractions; forming a thermal'crackinggas oil feed fraction having -a boiling range between 200 F. to -500 F. initial and 500 F. to 750 F. final, at least partly from gas oil sidestrearns withdrawn from said coker effluent fractionation zone and said catalytic cracking efiiuent fractionation zone; thermally cracking said thermal cracking fee'd'fraction at final temperatures of between 900 F. and 1100 F., quenching said efiiuent, and introducing it into a thermal cracking effluent fractionation zone; withdrawing overhead vapor fractions from said coker efliuent fractionation zone and said thermal efllucntfractionation zone, partially condensing them, and combining at least part of the uncondensed vapors remaining with said uncondensed vapors from said catayltic cracking effluent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said efiiuent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a lean gas and a rich oil; and returning said rich oil to at least one of said efiluent fractionation zones.

8. A continuous process for refining crude petroleumto produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and strai ht run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an effluent from said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said efiiuent into a vertically extended catalytic cracking efiluent fractionation zone operating at a temperature of between 90 F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said efliuent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking eflluent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation steps: heating it to temperatures of between 770 F. and 1000 F. and coking at least part to produce coke and coker hydrocarbon vapors having a find boiling point between 600 F. and 1100 F.; introducing coker hydrocarbon vapors into a coker efiluent fractionation zone without reduction in temperature of said efiluent below 780 F.; fractionating said coker efiiuent within said coker effluent fractionating zone under a pressure of less than 100 p. s. i. g. to obtain several fractions; forming a thermal cracking gas oil feed fraction having a boiling range between 200 F. to 500 F. initial and 500 F. to 750 F. final, at least partly from a gas oil sidestream withdrawn from one of said two previously mentioned effluent fractionation zones; thermally cracking said thermal cracking feed fraction at final temperatures of between 900 F. and 1100 F., quenching said efiiuent, and introducing it into a thermal cracking efliuent fractionation zone maintained at a pressure higher than said coker efiluent fractionation Zone and in a range of about 50 to 350 p. s. i. g.; withdrawing overhead vapor fractions from said coker effluent fractionation zone and said thermal effluent fractionation zone, partially condensing them, and combining at least part of the uncondensed vapors remaining with said uncondensed vapors from said catalytic cracking efiluent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said effiuent fractionation zones, countercurrently contactingsaid high pressure rich gas'with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a rich gas and a rich oil; and returning said rich oil to at least one of said effiuent fractionation zones.

9. A continuous process for refining crude petroleum to produce a maximum of light straight run products and crackedgasoline, which includes the steps of: continuously introducing said crude petroleum into a crude petroleum distillation zone and fractionating said crude petroleum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range of between 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between 0 and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contacting at least part of said heavy gas oil with finely di vided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an efiluent from said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said effluent into a vertically extended catalytic cracking efiuent fractionation zone operating at a temperature of between F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said efiluent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F. to 450 F. from the upper end of said catalytic cracking eflluent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation step; heating it to temperatures of between 7 70 F. and 1000 F. and coking at least part to produce coke and coker hydrocarbon vapors having a final boiling point between 600 F. and 1100 F.; introducing coker hydrocarbon vapors into a coker effluent fractionation zone without reduction in temperature of said efiluent below 780 F.; fractionating said coker efiluent within said coker efliuent fractionating zone to obtain several fractions; forming a thermal cracking gas oil feed fraction at least partly from a gas oil sidestream withdrawn from one of said two previously mentioned effiuent fractionation zones; introducing said thermal cracking feed fraction into a thermal cracking efiiuent fractionation zone; withdrawing a sidestream having a boiling range between about 200 F. to 500 F. initial and 5 00 F. to 7 50 F. final from said zone; thermally cracking said thermal cracking efiiuent fractionation zone sidestream at final temperatures of between 900 F. and 1100 F., quenching said efiiuent, and returning it to said thermal cracking efiiuent fractionation zone; withdrawing overhead vapor fractions from said coker effluent fractionation zone and said thermal effluent fractionation zone, partially condensing them, and combining at least part of the uncondensed vapors remaining with said uncondensed vapors from said catalytic cracking etfluent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said eflluent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a rich gas and a rich oil; and returning said rich oil to at least one of said eliiuent fractionation zones.

10. A continuous process for refining crude petroleum to produce a maximum of light straight run products and cracked gasoline, which includes the steps of: continously ntro uc n s id crude Pet ole m nto a c straight run iiractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum dis.- tillation gone at a pressure between and 50 p. s. i. g. and

V a temperature between 500 F. and 800 F. and contacting atleast part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperature of said heavy gas oil below 450. F., and catalytically cracking said oil; withdrawing an eflluentfrom said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said effiuent into a vertically extended catalytic cracking effluent fractionation zone operating at a temperature of between 90 F. and 200 F. at the top, and 600 F. to

900 F. at the bottom, and a pressure of between 0 and 50 p, s. i. g. without reduction in temperature or pressure of said efiluent below 600-F. and 0 p. s. i, g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range ending at from 250 F;

to 450 F. from the upper end of said catalytic cracking eflluent fractionation zone, cooling to partially condense said efliuent, compressing the uncondensed portion and pumping the condensed portion to higher pressures; withdrawing said rednced crude from said crude petroleum fraction derived from said heated vacuum fraction to a vertically extended combination fractionation zone; fractionating vapors Within said combination fractionating zone under a pressure of to 350 p. s. i. g. to obtain several fractions, including a light gas oil fraction having a boiling range between 200 F.'to 500 F. initial and 500 F. to 750 F. final; withdrawing said light gas oil fraction from said combination fractionating zone, thermally crackingsaid light gas oil fraction at final temperatures of between 900 F. and 1100 F.; introducing effluent from said thermal cracking into said combination fractionating zone; withdrawing from said combination fractionating zone a heavy gas oil having a boiling range between 450 F. and650 F. initial and 700 F. and 1000 F. final, and recycling said heavy gas oil to at least one of said heating steps; withdrawing a fraction composed primarily of gasoline from the upper end of said combination fractionating zone, cooling it to partially condense said fraction; forming a stream of rich gas derived at least in part from said uncondensed portions taken from said catalytic cracking efiluent fractionating zone and said combination fractionating zone; forming a stream of lean. light gas oil at least partly by withdrawing a stream having a boiling range of between 300 F. to 500 F. initial and 600 F. to 750 'F. final boiling point from at least one of said effluent fractionation zones; countercurrently contaeting said high pressure rich gas with said stream of ea. li h as o l o ab orb heavier hydrocarbons f said rich gas and thereby produce a lean gas and a rich oil; and returning said rich oil to at least one of said eflluent'fractionation zones. V

11. A continuous process for refining crude petroleum o pr uce maxim m of l ht a h n pr u d c cked ga oli e. h ch n l e he st p nt nu u ly gtr dus ne sa d 9419? P roleum int a rud pe ol um is i lat n on d f fl wa i i de P ro eum therein into a reduced crude fraction having an initial boiling range starting between 400 F. and 900 F., a gas oil fraction having a boiling range ofbetween 300 F. to 700 F. initial, and 600 F. to 1100 F. final, and straight run fractions of lower boiling range; continuously withdrawing said gas oil from said crude petroleum distillation zone at a pressure between 0 and 50 p. s. i. g. and a temperature between 500 F. and 800 F. and contactat least part of said heavy gas oil with finely divided solid catalyst at cracking temperatures and pressures without reducing the temperatureof said heavy gas oil below 450 F., and catalytically cracking said oil; withdrawing an efiluent from said catalytic cracking step at a temperature of between 850 F. and 1000 F., and introducing said efiluent into a vertically extended catalytic cracking effluent fractionation zone operating at a temperature ofbetween F. and 200 F. at the top, and 600 F. to 900 F. at the bottom, and a pressure of between 0 and 50 p. s. i. g. without reduction in temperature or pressure of said eflluent below 600 F. and 0 p. s. i. g. respectively, prior to said introduction; withdrawing a light gaseous fraction having a boiling range endingat from 250 F. to 450 F. from the upper end of said catalytic cracking effluent, compressing the uncondensed portion and pumping'thecondensed portion to higher pressures; withdrawing said reduced crude from said crude petroleum fractionation step; separating it into light and heavy vacuum fractions by vacuum distillation; diverting at least part of said light vacuum fractions to said catalytic cracking step; subjecting said heavy vacuum fraction to heating to temperatures in the coking and vis-breaking range; passing at least a fraction derived from said heated heavy vacuum fraction to a second efliuent fraction zone; fractionating vapors within said second effluent fractionation. zone to obtain several fractions; forming a thermal crack- 7 ing gas oil feed fraction having a boiling range between 200 F. to 500 F. initial and 500 F. to 750 F. final, at least partly from a gas oil sidestream withdrawn from one of said two previously mentioned efiluent fractionation zones; thermally cracking said thermal cracking feed fraction at final temperatures of between 900 F. and 1100 F., quenching said etiluent, and introducing it into a thermal cracking effluent fractionation zone; Withdrawing overhead vapor fractions from said second'effluent fractionation zone and said thermal cracking fractionation zone, partially condensing them, and combining at least part of the uncondensed vapors remaining with said uncondensed vapors from said catalytic cracking efliuent fractionation zone to make up at least part of a rich gas under pressure; forming a stream of lean light gas oil by withdrawing a stream having boiling range of between 300 F. to 500 F. initial and 600 F. to 750 F. final boiling point from at least one of said eflluent fractionation zones, countercurrently contacting said high pressure rich gas with said stream of lean light gas oil to absorb heavy hydrocarbons from said rich gas and thereby produce a rich gas and a rich oil; and returning said rich oil to at least one of said efhuent fractionation zones.

References Cited in the tile of this patent UNITED STATES PATENTS 2,222,275 Babcock Nov. 19, 1940 2,285,606 Nofsinger June9, 1942 2,345,129 Kuhn Q Mar. 28, 1944 2,366,218 Ruthruff Jan. 2, 1945 2,497,421 Shiras Feb. 14, 1950

Claims

1. A CONTINUOUS PROCESS FOR REFINING CRUDE PETROLEUM TO PRODUCE A MAXIMUM OF LIGHT STRAIGHT RUN PRODUCTS AND CRACKED GASOLINE, WHICH INCLUDES THE STEPS OF: CONTINUOUSLY INTRODUCING SAID CRUDE PETROLEUM INTO A CRUDE PETROLEUM DISTILLATION ZONE AND FRACTIONATING SAID CRUDE PETROLEUM THEREIN INTO A REDUCED CRUDE FRACTION HAVING A BOILING RANGE STARTING BETWEEN 400* F. AND 900* F., A HEAVY GAS OIL FRACTION HAVING A BOILING RANGE OF BETWEEN 300* F. TO 700* F. INITIAL AND 600* F. TO 1100* F. FINAL, AND STRAIGHT RUN FRACTIONS OF LOWER BOILING RANGE; CON-