Process For The Production Of Olefinically Unsaturated Hydrocarbons

Abstract

Hydrocarbon feedstock containing petroleum residuum is catalytically cracked in a heavy oil cracking unit to produce a naphtha feed suitable for processing by steam pyrolysis to olefins. By the process integration disclosed, internal gas compression energy requirements for olefins recovery are furnished by steam generated in the heavy oil cracking unit.

Description

This invention relates to the integration of fluid catalytic cracking of heavy hydrocarbon oils containing petroleum residuum and thermal pyrolysis of hydrocarbons to produce olefinically unsaturated hydrocarbons such as ethylene and propylene.

Heretofore, it has been known to convert naphtha, ethane, or porpane feedstocks to olefins by themal pyrolysis with steam. Conventional processes are broadly disclosed in the Nov. 13, 1965 issue of "Chemical Week," pages 70-80.

It has also been known to fractionate a crude petroleum oil and pyrolytically convert selected distillate fractions to olefins according to U.S. Pat. No. 3,409,540. In this process, however, residuum from such fractionation is diverted to fuel oil use and no attempt is made to derive pyrolysis feed from it. Moreover, in order to minixmize residum production, a heavy gas oil cut form the fractionator is hydrocracked and certain separation products from hydrocracking are thereby rendered suitable for pyrolysis feed.

In a related process disclosed in U.S. Pat. No. 3,617,495, residuum from crued oil distillation is coked and coker naphtha so produced is made suitable for pyrolysis feed by hydrotreatment. In this process, however, relatively large amounts of fuel oil are produced from the distillation zone and from the coker. The coke and fuel oil resulting from these operations cannot be readily utilized in ethylene production.

It is an object of this invention to provide a more efficient and less expensive process for the manufacture of olefins and aromatic compounds. Another object of the invention is to integrate catalytic cracking of heavy hydrocarbons with thermal pyrolysis of light hydrocarbon feeds to efficiently produce olefins and aromatic compounds. Another object of the invention is to provide a process for olefins production from residual feedstocks. Yet another object of this invention is to provide internal compression energy requirments for recovery of olefins produced by thermal pyrolysis from components of crude petroleum oil that are unsuitable pyrolysis feeds. Further objects and advantages of the invention will be apparent from the drawings and the following description.

According to the invention, a heavy hydrocarbon containing petroleum residuum is converted to cracked products including naphtha in a heavy oil cracking unit having a fluid catalytic cracking zone and a catalyst regenreration zone. The naphtha is passed to a non-catalytic thermal pyrolysis zone and converted to thermally cracked effluent containing large quantities of olefins having from 2 to 4 carbon atoms. The olefins are recovered in a known manner by process gas compression and refrigeration. In addition, high pressure steam is produced in the regeneration zone of the heavy oil cracking unit and the steam so produced is utilized in olefins recovery.

FIG. 2 is a schematic diagram of a petrochemical refinery and discloses the production of C.sub.2 -C 4 olefins and aromatic compounds from crude petroleum oil wherein a substantial part of the thermal pyrolysis feed is derived from a residue fraction of the crude oil.

FIG. 3 is a schematic diagram of steam generation and use within the petrochemical refinery concept of FIG. 2 and discloses a total energy concept with fulfillment of the entire gas compression energy requirements of the process through internal process generation of steam with consequent fuel and power savings.

The heavy oil cracking (HOC) unit comprises a fluid catalytic cracking zone 1 and a catalyst regeneration zone 2. Fluidized cracking catalyst circulating between the two zones may be of conventional type such as activated clay, silica-alumina, silica-zirconia, and alumina-boria, however, natural and synthetic zeolitic catalysts, particularly of the molecular sieve, matrix type having an average particle size range of from about 40 to about 100 microns, are preferred cracking catalysts.

The catalytic cracking zone 1 is preferably a transfer line reactor and is most preferably a riser reactor of the type described in U.S. Pat. No. 3,607,127. The riser type unit is more fully depicted in FIG. 2 of the drawings.

In operation of the HOC unit, residue containing hydrocarbon feedstock is fed to the lower part of the riser reactor at a temperature of from about 150.degree.F to about 750.degree.F and is admixed with the cracking catalyst in the presence of fluidizing steam. Typical cracking conditions include a temperature range from about 850.degree.F to about 1,200.degree.F, pressure from about 10 psig. to about 50 psig., catalyst to oil ratio of from about 3:1 to 15:1, and space velocity of from about 0.5 to 1,000. Normally from 50 to 95 percent of the cracking reaction takes place in the riser reactor with the remainder occurring in the disengaging and stripping zones located generally in the upper part of the heavy oil cracking unit. Cracked effluent including a cracked naphtha fraction leaving the riser reactor disengages from catalyst in the upper part of the HOC unit and exits through a series of cyclone separators that return entrained catalyst to a fluid bed regeneration zone below the disengaging zone. Severe cracking conditions are employed in order to maximize conversion of the feedstock to naphtha boiling range hydrocarbons for thermal pyrolysis feed. Generally, at least 65 volume percent and most preferably 80 to 100 percent of the feed is cracked to light hydrocarbons boiling in the naphtha range, gases including hydrogen, cycle oil, and coke.

Following disengagement from cracked effluent, catalyst contaminated with coke and occluded hydrocarbons passes downwardly through a stripping zone. The stripping zone is fitted with suitable baffling and steam sparging means to strip occluded cracked effluent which passes over head while catalyst coated with coke and some non-volatile hydrocarbons passes downwardly into regeneration zone 2 located in the lower part of the HOC unit.

In the regeneration zone catalyst is contacted with an oxygen-containing gas, preferably air, furnished by a regenerator air blower or compressor (see reference numeral 46 in FIG. 2). Air furnished by this blower will normally be at a pressure of from about 20 psia. to about 70 psia. and delivered at a rate of from about 11 pounds to about 13 pounds per pound of coke burned from the catalyst. The air delivery rate is varied in order to maintain regeneration zone temperatures of from about 1,000.degree.F to about 1,400.degree.F and at which temperature materials coated on the catalyst are burned off to desired levels of residual coke on regenerated catalyst. Such levels will generally be from about 0.05 to about 0.4 weight percent, preferably from about 0.05 to about 0.15 weight percent. Following regeneration, catalyst is returned to the riser reactor.

In view of the generally high carbon content of residue fractions processed by the HOC unit and the formation of additional carbon or coke during cracking, coke deposits on the cracking catalyst will normally be heavy. Due to combustion of this carbon, a substantial amount of heat is evolved during regeneration of cracking catalyst which is recovered through indirect heat exchange as high pressure steam, preferably at a pressure of from about 1,000 psia. to about 2,000 psia. by introducing boiler feed water to steam coils or tubes located within the regeneration zone (see reference numerals 50, 51, and 52 in FIG. 2). In most instances the steam coils will be interconnected to a suitable flash drum and auxiliary equipment (not shown).

High pressure steam so produced is utilized in expansion turbine drives shown generally be reference numeral 3 employed in gas compression required for olefins recovery. In an integrated petrochemical refinery as shown in FIG. 2, later described, the quantity of high pressure steam from the regeneration zone of the HOC unit is sufficient to provide at least a major part of the gas compression energy requirements of the process and will generally provide about two-thirds of this requirement in terms of the weight flow rate of steam generated and expanded in compressor turbine drives. The term gas compression energy is intended to mean the total energy expended in compressing pyrolysis effluent gas to the pressure required for olefins recovery in addition to te refrigeration compression required for chilling pyrolysis effluent in order to perform product separations by fractionation. Generally, the compression energy required for these purposes will be about equally divided between process gas compression and refrigeration compression. High pressure steam may drive turbo-generators and indirectly provide such gas compression energy requirements through electro-mechanical means, however, direct steam turbine drives to the compressors will generally be preferred.

A major part of the steam expanded through the turbines is condensed and recycled through a boiler feed water system. Preferably, a portion of this steam is further expanded to reduced pressure ranging from about 100 psia. to about 200 pisa. for use as steam diluent of hydrocarbon feed to thermal pyrolysis zone 4.

A cracked naphtha fraction separated from catalytically cracked effluent leaving the HOC until may be passed directly to thermal pyrolysis zone 5, however, the fraction will normally contain olefinic materials that tend to form coke and to polymerize excessively when subjected to pyrolytic conversion. Preferably the cracked naphtha fraction is hydrotreated, as will be later described. The cracked naphtha fraction is then admixed with diluent steam from the expansion turbines and introduced to thermal pyrolysis zone 5 which will be subsequently discussed in connection with FIG. 2.

Thermally cracked effluent from the pyrolysis zone is then cooled and passed to process gas compression zone 6 and pressurized to from about 400 psia. to about 650 psia. to facilitate fractionation of products. Separations of hydrogen, fuel gases, ethane, propane, mixed C.sub.4 compounds, and products including ethylene and propylene are than performed in product recovery zone 7 by known chilling and separation steps . A typical separations process is described in the Nov. 13, 1965 issue of "Chemical Week," 77-80.

In a preferred embodiment the integrated process is carried out according to the following example.

Referring now to FIG. 2, 690,000 1lb./hr. of desalted whole petroleum crude oil containing 2.6 weight percent sulfur is introduced through line 25 to thermal distillation zone 26. A gaseous overhead fraction comprising predominantly C.sub.3 and C.sub.4 paraffinic hydrocarbons is removed through line 27. A straight-run naphtha fraction boiling between about 85.degree.F and about 450.degree.F is removed from the distillation zone through lines 28 and 34 and passed to thermal pyrolysis zone 35. A light gas oil fraction boiling in the range from about 300.degree.F to about 650.degree.F is also removed from the distillation zone and passed through lines 29 and 34 to pyrolysis zone 35. A heavy gas oil fraction boiling in the range from about 550.degree.F to about 1,000.degree.F is removed from a lower section of the distillation zone through line 30 and hydrodesulfurized in zone 31 with hydrogen introduced through line 32. The hydrodesulfurizer may utilize cobalt-molybdenum or alumina catalyst and is operated at temperatures ranging from about 550.degree.F to 750.degree.F and pressure ranging from about 200 psia. to about 600 psia. Desulfurized gas oil is then passed to the thermal pyrolysis zone through lines 33 and 34. If desired, portions of the naphtha or gas oil fractions may be diverted to other uses, however, in an integrated petrochemical refinery of the type described herein, it is preferred to pass these fractions to the thermal pyrolysis zone in order to maximize olefins and aromatic hydrocarbons production.

From the bottom of thermal distillation zone 26, 365,000 1lb./hr. of a petroleum residuum fraction boiling above about 600.degree.F is removed through line 36 and passed through line 37 to catalytic cracking zone 38 of heavy oil cracking unit 39. The catalytic cracking zone in FIG. 2 is illustrated as a riser reactor.

Alternately, all or part of the residue fraction from thermal distillation zone 26 may be passed through a solvent deasphalting zone, for example a propane deasphalting unit, to obtain a deasphalted oil which is subsequently charged to the HOC unit. This step will generally not be used when asphaltene and metals content of the residue fraction is not excessively high.

The residuum fraction is fed to the lower part of riser 38 to a temperature of from about 150.degree.F to about 750.degree.F and is admixed with circulating, regenerated cracking catalyst and with fluidizing steam introduced from line 40 at about 100 psia. Cracked effluent including a cracked naphtha fraction laeaving riser 38 disengages from the catalyst in disengaging zone 41 and passes upwardly through cyclones (not shown) for recovery through line 43.

Catalyst with coke and occluded hydrocarbons deposited thereon passes downwardly through the disengaging zone to stripping zone 42 for removal of occluded hydrocarbons which pass overhead with the cracked effluent. Stripped catalyst then passes to regeneration zone 44 where coke and non-volatile hydrocarbonaceous materials are burned from the catalyst with air introduced through line 45 from regenerator air blower 46. Flue gases containing carbon monoxide from the regeneration step leave zone 44 through line 47 for further use and treatment.

Heat produced during regeneration is removed by passing boiler feed water through line 50 to coils 51 located within the regeneration zone and thereby producing steam by indirect heat exchange at a high pressure of about 1,500 psia. which is removed at a rate of 650,000 1lb./hr. through line 52.

Cracked effluent removed from the HOC unit through line 43 is introduced to cracker fractionator 53 at a temperature of about 1,000.degree.F and pressure of about 20 psia. A volatitle overhead stream comprising hydrogen and paraffinic hydrocarbons lighter than C.sub.4 is removed from the cracker fractionator through line 54. In conventional refinery operations, C.sub.2 and lighter materials would be used as plant fuel or compressed and diverted to other process facilities. Here, the stream is combined with overhead in line 27 from thermal distillation zone 26 and integrated into olefins production as later described.

Decant oil is removed from the bottom of a cracker fractionator 53 through line 55 and is preferably passed to catalytic cracking zone 38 of the HOC unit through line 37. Alternately, all or a part of this oil may be diverted to other uses, for example, carbon black production or auxiliary fuel. A cycle oil suitable for further processing to commercial fuel oil is removed by way of line 56.

The principal product of the HOC unit, a cracked naphtha fraction boiling between about 85.degree.F and about 450.degree.F is removed from the cracker fractionator through line 57 at the rate of 127,000 lb./hr. and passed to hydrotreating zone 58 for olefins saturation and desulfurization in the presence of a catalyst with hydrogen introduced to the hydrotreating zone. Additionally, 92,000 lb./hr. of pyrolysis gasoline from downstream process sources later described is passed to hydrotreatment zone 58 for similar processing. Hydrotreating will serve to prepare the feed for pyrolytic conversion by saturating olefins, partially saturating aromatic compounds, and by removing sulfur contained in the fraction by hydrodesulfurization. A substantial part of the hydrogen required in hydrotreating may be obtained from the hydrogen produced in the HOC unit and later recovered in the product separation zone.

Hydrotreating is generally performed in one or more stages at temperatures ranging from about 450.degree.F to about 800.degree.F and pressures from about 100 psia. to 1,500 psia. Preferred hydrotreating catalysts comprise one or more hydrogeneration metals supported on a suitable carrier material. Oxides or sulfides of molybdenum, tungsten, cobalt, nickel, and iron supported on such supports as alumina and silica-alumina are used. The most preferred catalysts are cobalt molybdate or alumina and nickel molybdate on alumina. The catalyst can be employed in the form of a fixed bed or a fluidized bed. Liquid phase or mixed phase conditions can be used. Space velocities are from about 1 to about 15 volumes of feed per volume of catalyst per hour and hydrogen addition rates are from about 50 to about 2,000 SCF/bbl. A number of hydrogen treating processes of varying degrees of severity are disclosed in "Hydrocarbon Processing," September 1972, pages 150-184.

A hydrotreated naphtha fraction containing predominantely C.sub.5 paraffinic hydrocarbons is recovered from the hydrotreating zone and passed through line 59 to thermal pyrolysis zone 35 at the rate of 35,000 lb./hr.

A hydrocarbon stream containing naphtha and aromatic compounds is also separated in hydrotreating zone 58 and passed through line 60 to an aromatics extraction and separation zone 61 which may typically utilize solvent extraction by, for example, ethylene glycol, furfural, or dimethyl formamide. Proudct separations in extraction zone 61 yields 39,000 lb./hr. of benzene, 24,000 lb./hr. of toluene, and 12,000 lb./hr. of xylene. 104,000 lb./hr. of paraffinic raffinate resulting from aromatics extraction is then passed through lines 62 and 59 to thermal pyrolysis zone 35.

Thermal pyrolysis zone 35 contains pyrolysis furnaces adapted fro steam cracking of hydrocarbons varying from light paraffins to gas oils to produce C.sub.2 to C.sub.4 olefins. In FIG. 2, the thermal pyrolysis feed steams previously described are mixed with 310,000 lb./hr. of diluent steam from line 63 at a pressure of about 150 psia. Such steam is obtained from the discharge of gas compressor turbines as later described. Diluent ratios are about 0.6 pounds of steam per pound of naphtha feed, and 0.75 pounds of steam per pound of gas oil feed. It is understood that individual furnaces within the thermal pyrolysis zone may vary somewhat in detail design to suit the particular feed streams involved. Typically, a pyrolysis furnace will contain convection heating coils in which feed materials are preheated to temperatures as high as 1,200.degree.F and radiation sections in which preheated feed is converted to olefins in the presence of diluent steam at temperatures in the range of about 1,400.degree.F to about 2,000.degree.f depending on the feedstock used and product mix desired. Residence time of hydrocarbons in the furnaces is low, generally from about 0.2 seconds to about 2.0 seconds and maybe as low as 0.01 seconds.

Thermally cracked effluent containing C.sub.2 -C.sub.4 olefins, pyrolysis gasoline, pryrolysis oil, hydrogen, and light paraffins is passed from the thermal pyrolysis zone through line 64 to quench zone 65 where the effluent is rapidly cooled to a temperature of from about 600.degree.F to about 1,000.degree.F depending on the pyrolysis feedstock. Boiler feed water is introduced to the quench zone and passed in indirect heat exchange with the thermally cracked effluent to produce 542,000 lb./hr. of steam at a pressure of about 1,500 psia. which is removed through line 66.

Thermally cracked effluent is passed from quench zone 65 through line 67 to effluent fractionator 68 where a pyrolysis oil bottoms fraction is removed and passed to the catalytic cracking zone 38 of the heavy oil cracking unit 39 at the rate of 43,000 lb./hr. through lines 69, 36, and 37. An overhead fraction containing the oil-depleted thermally cracked effluent is recovered from the effluent fractionator through line 70 at a pressure of about 7 psig. and admixed with light hydrocarbons contained in lines 27 and 54. the combined effluent stream is then passed through line 27 to a process gas compression zone 71 where pressure is increased from 7 psig. to 550 psia. in order to facilitate product separations. a pyrolysis gasoline stream containing aromatic compounds, principally aromatic hydrocarbons such as benzene, toluene, and the xylenes, is separated from combined effluent in the gas compression zone 71 and passed through line 72 to previously described hydrotreating zone 58.

Following compression and pyrolysis gasoline removal, the combined effluent is passed through line 73 to acid gas separation zone 74 for removal of carbon dioxide and hydrogen sulfide, thence through line 75 to drying zone 76, and then through line 77 to chilling zone 78 where the effluent stream is cooled by refrigeration supplied from refrigeration compressors 79. Hydrogen is removed from chilling zone 78 through line 80 at the rate of 7,000 lb./hr. This hydrogen is utilized in hydrotreating zone 58, hydrodesulfurization zone 31, and may be used for desulfurization of fuel oil separated in the cracker fractionactor 53.

chilled pyrolysis effluent is then passed through line 81 to product separation zone 82 where 152,000 lb./hr. of ethylene, 81,000 lb./hr. of propylene, and 91,000 lb./hr. of mixed C.sub.4 hydrocarbons are spearated by fractionation and removed as products of the process. Additionally, 38,000 lb./hr. of ethane and 14,000 lb./hr. of propane are removed from the product recovery zone and recycled via lines 83, 59, 33, and 34 to thermal pyrolysis zone 35. A residual stream of pyrolysis gasoline is also removed through line 84 and passed to hydrotreating zone 58.

A preferred embodiment of the total energy concept of the invention follows.

Referring now to FIG. 3, which illustrates steam integration with olefins production from crude oil, processing zones are those previously described for FIG. 2, however, many of the interconnecting process lines have been omitted for clarity.

Steam at a high pressure of about 1,500 psia. is recovered from the regeneration zone 44 of the HOC unit 39 as previously described and delivered at the rate of 650,000 lb./hr. through line 52 to high pressure steam header designated by reference numeral 85.

Additionally, 542,000 lb./hr. of 1,500 psia. steam is recovered from quench zone 65 and delivered through line 66 to high pressure steam header 85.

Since flue gas produced from the oxidation of coke in the HOC unit regeneration zone will normally contain an appreciable amount of carbon monoxide, it is preferably passed to CO boiler 48 and burned with the aid of a high heat value fuel such as recovered fuel gas to generate high pressure steam from boiler feed water. All or part of the steam thus produced may be used in fulfilling the remaining energy requirements of the process, providing energy required by the regenerator air blower, or exported as a product of the process. Accordingly, 650,000 lb./hr. of 1,500 psia. steam is recovered from the CO boiler 48 and delivered through line 49 to high pressure steam header 85.

100,000 lb./hr. of the high pressure steam from header 85 is passed through line 86 and expanded through regenerator air blower 46. Steam exhausted from turbine 87 is then returned through line 92 to boiler feed water recovery system 93 where it is condensed, treated and repressurized for distribution by suitable lines (not shown) to the previously described steam generation zones.

High pressure steam is similarly passed from header 85 through line 88 at the rate of 281,000 lb./hr. to refrigeration zone turbines 89 which are mechanically connected to closed loop refrigeration compressors shown generally by reference numeral 79. Steam exhausted from these turbines is also returned through line 92 to feed water recovery system 93.

678,000 lb./hr. of high pressure steam is passed from header 85 through line 90 to process gas turbine 91 which is mechanically connected to process gas compressor 71. A minor portion of this steam is returned through line 92 at the rate of 155,000 lb./hr. to feed water recovery system 93. Since high pressure steam produced in the regeneration zone 44, quench zone 65, and CO boiler 48 is in excess of the gas compression energy requirements of the process and the regenerator air blower requirement, 738,000 lb./hr. of high pressure steam is exported by way of lines 85 and 96 as a product of the process.

A major portion of the steam entering turbin 91 is partially expanded to a medium pressure of about 450 psia. and passed through line 94 at the rate of 523,000 lb./hr. to medium pressure steam header 95. It is understood that an equivalent amount of steam expanded to the medium pressure may be exhausted from any of the high pressure steam turbines according to the specific conditions involved.

210,000 lb./hr. of steam from header 95 is further reduced in pressure to about 150 psia. through valve 97 and combined with 100,000 lb./hr. of steam from line 98 that is produced at approximately the same pressure in cracker fractionator boiler 99 which removes heat from catalytically cracked effluent by recirculation of the fractionator bottom contents. The combined stream is then passed through line 63 to thermal pyrolysis zone 35 for use as process diluent stream.

The remaining medium pressure steam is delivered through line 95 and 100 to other internal process uses such as pump drives, process heating, and fluidizing steam for the HOC unit.

Thus, the process embodiments of the present invention provide a means for the conversion of heavy hydrocarbons to olefins and aromatic compounds. Whole crude oil and petroleum fractions containing substantial amounts of sulfur and metals can be converted to desirable products such as ethylene, propylene, benzene, toluene, and the xylenes. The heavy oil cracking concept of the present invention is unique in that a residuum containing hydrocarbon may be converted and treated to a feedstock suitable for pyrolitic conversion to olefins in the presence of steam.

The embodiments of the invention are essentially selfsupporting from an energy balance standpoint. The heavy oil cracking unit provides very large quantities of steam which are utilized to provide a major part of the gas compression energy requirements of the process. In the petrochemical refinery embodiment of the present invention, all of the internal gas compression energy and heat requirements of the process are furnished from the heavy oil cracking unit and the thermal pyrolysis quench zone and substantial quantities of high pressure steam are exported as a product of the process. The feed to the heavy oil cracking unit may be recycled to extinction or a portion of the recycle material can be used as plant fuel. The quantity of hydrogen required to saturate and desulfurize the various intermediate fractions produced in the preferred embodiments is much less than the quantity of hydrogen which would be required to support a hydrocracking unit and associated hydrodesulfurization units.

Obvious variations of process embodiments disclosed in the drawings and the foregoing descriptions are intended to be included within the scope of the disclosure and claims.

Claims

1. A process for the production of olefinically unsaturated hydrocarbons which comprises the steps of:

a. introducing a hydrocarbon feedstock comprising petroleum residuum into the catalytic cracking zone of a heavy oil cracking unit in the presence of fluidized cracking catalyst at cracking conditions to produce a catalytically cracked effluent including a cracked naphtha fraction;

b. regenerating said fluidized cracking catalyst in the regeneration zone of the heavy oil cracking unit;

c. producing high pressure steam in said regeneration zone by indirect heat exhange;

d. passing the cracked naphtha fraction to a thermal pyrolysis zone and thermally cracking said fraction to produce a thermally cracked effluent containing olefinically unsaturated hydrocarbons;

e. expanidng said high pressure steam from step (c) to provide at least part of the gas compression energy required for recovery of the olefinically unsaturated hydrocarbons; and

2. The process of claim 1 wherein at least a portion of the expanded high pressure steam is mixed with the cracked naphtha fraction fed to the

3. The process of claim 1 wherein the catalytic cracking zone includes a

4. The process of claim 1 wherein the olefinically unsaturated hydrocarbon

5. The process of claim 1 wherein the hydrocarbon feedstock is crude

6. The process of claim 1 wherein the hydrocarbon feedstock is a pertroleum

7. The process of claim 1 wherein the hydrocarbon feedstock is an

8. An integrated process for the production of olefinically unsaturated hydrocarbons and aromatic compounds comprising the steps of:

a. introducing hydrocarbon feedstock containing petroleum residuum into the catalytic cracking zone of a heavy oil cracking unit in the presence of fluidized cracking catalyst at cracking conditions to produce catalytically cracked effluent including a cracked naphtha fraction;

b. passing the cracked naphtha fraction to a thermal pryrolysis zone at thermal cracking conditions to produce a thermally cracked effluent containing pyrolysis oil, olefinically unsaturated hydrocarbons and aromatic compounds;

c. separating pyrolysis oil from the thermally cracked effluent;

d. passing pyrolysis oil to the catalytic cracking zone of the heavy oil cracking unit; and

e. recovering olefinically unsaturated hydrocarbons and aromatic compounds.

9. An integrated process for the production of olefinically unsaturated hydrocarbons comprising the steps of:

a. introducing hydrocarbon feedstock containing petroleum residuum into the catalytic cracking zone of a heavy oil cracking unit in the presence of fluidized cracking catalyst to produce a catalytically cracked effluent including a cracked naphtha fraction;

b. regenerating said fluidized cracking catalyst in the regeneration zone of a heavy oil cracking unit;

c. producing high pressure steam in said regeneration zone by indirect heat exchanage;

d. passing the cracked naphtha fraction to a thermal pyrolysis zone to produce a thermally cracked effluent containing olefinically unsaturated hydrocarbons;

e. cooling thermally cracked effluent in a quench zone;

f. producing high pressure steam in the quench zone by indirect heat exchange;

g. exapnding high pressure steam from steps (c) and (f) to provide the gas compression energy required for a recovery of olefinically unsaturated hydrocarbons; and

10. The process of claim 9 wherein a portion of the expanded high pressure

11. The rpocess of claim 9 wherein

a. flue gas is recovered from the regeneration zone and passed to a carbon monoxide boiler;

b. high pressure steam is produced in the carbon monoxide boiler; and

c. high pressure steam is recovered as a product of the process.