US2207598A - Cracking hydrocarbon oils - Google Patents

Description

CRACKING HYDROCARBON OILS Filed June 29, 1937 wscas/rraitmv yagrrpcnupza/L 1. 167/ f an: 04 c/ucmva @011.

INVENTOR ROBERTE/PUT/llPl/FF ATTORNEY Patented July 9, 1940 UNITED STATES CRAOKIN G HYDBOCABBON OILS Robert F. Ruthnifl', Nutley, N. J.,. asaignor to Standard Oil Company. Chicago, 111., a corporation of Indiana ap i'icaiionsune 29, 1931. serial No. 150,894

2 Claims.

This invention relates to certain new and useful improvements in combination cracking processes. The invention has in view the provision of a-combination process in which the constituent elements of the crude petroleum are treated in a practical way in a complete unitary operation which shall be highly eflicient in attainin the ultimate object of a maximum yield of gasoline of maximum anti-knock quality.

In accordance with the invention crude petroleum is subjected to fractionation to separate it into a residue which is subjected to viscositybreaking and into a plurality of condensate or distillate fractions which are subjected to sep arate cracking treatments. The products of the viscosity-breaking operation are fractionated separately from the products of the other cracking operations so as to thus segregate the rela- .tively low anti-knock viscosity-broken gasoline as well as other distillates for cracking in the several cracking units of the system. The crude residuum is subjected to cracking under viscositybreaking conditions in a single-pass or oncethrough operation and the gas oil constituents produced in the viscosity-breaking operation are for breaking operations subjected to cracking in another recycling cracking zone, the products from both cracking zones being fractionated to form a primary reflux condensate which is cycled to the heavygas oil cracking zone and a secondary reflux condensate which is cycled to the light gas oil cracking zone. In this method of operation the fractions directed into the light gas oil cracking zone may well include gasoline constituents so that the reforming of the gasoline constituents may be accomplished.

In a modification contemplated by the invention the gasoline constituents of the crude oil as well as gasoline constituents produced in the viscosity-breaking operation, instead of being included in the charge to the light gas oil cracking zone, are directed into a separate reforming zone in which the gasoline constituents are subjected to reforming conditions in a single-pass or oncethrough cracking operation. The once-through reforming operation is advantageous in accomplishing the desired extent of reforming while avoiding deterioration in anti-knock value of reformed constituents. The reformed products may be subjected to fractionation together with the cracked products from the light gas oil and heavy gas oil cracking zones and thus the distillate polymer products formed in the reforming operation will be cycled to either the light gas oil or heavy gas oil cracking zones, where they may be subjected to further cracking more advantageously-than by cycling them to the reforming zone.

15 In order to explain the invention in greater detail, reference will now be had to the accompanying drawing which is a flow diagram illustrating the invention.

Referring to the flow diagram, heated crude oil which has ben raised to a desired distilling temperature, as by means of heat exchange of cracked products from the process or by heating in an economizer section of the furnaces supplying heat to the cracking coils, is intoduced through line It into an evaporator and fractionating tower II. The tower is provided with trap-out trays as l2, II and H for the collection of the desired fractions and with a condenser coil l5 and receiving drum it for the overhead distillate.

Residue from the tower H is withdrawn by a pump I1 and charged to a viscosity-breaking coil l8 positioned in a furnace IS. The viscositybroken products pass to a separator 20 from which the separated vapors pass to a series of fractionating towers 2!, 22 and 23, overhead vapors from the last tower passing to a condenser coil 24 discharging into a distillate receiving drum 2!.

Primary reflux condensate such as gas oil is withdrawn from trap-out tray l2 of tower II by means of line 26 and pump 21 and charged to a cracking coil 28 positioned in furnace 29. Primary reflux condensate from the viscosity-breaking operation is withdrawn from primary tower 2| by means of line 30 and pump 3| for introduction tothe heating coil 28. The cracked products from the cracking coil 28 pass through transfer line 32 to a separator 33.

Secondary reflux condensate such as light gas oil is withdrawn from trap-out tray ii of the stripping tower II by means of line 34 and pump 35 and charged to cracking coil 36 positioned in furnace 31. Secondary reflux condensate from u the viscosity-breaking operation is withdrawn from tower 22 by means of line 38 and pump 88.

and charged to the heating coil 36. The stocks charged to cracking coil 36 should be stocks that are substantially completely vaporizable so that they will be well adapted for vapor phase cracking under conditions of high rates of cracking per pass to effect conversion into gasoline constituents. of high anti-knock value. In the vapor phase cracking operation it is advantageous to operate with a reaction chamber in which the products which have been heated to a high crack- 'ing temperature in the heating coil may be subjected to further conversion, and accordingly the transfer line 40 from the vapor phase cracking coil 36 preferably extends to a reaction chamber 41 from which a transfer line 42 leads to the separator 33.

A naphtha or gasoline fraction is withdrawn from trap-out tray i4 of the crude fractionating tower by means of line 43 and pump 44 and charged to a naphtha reforming coil 45 positioned in furnace 46. The line 43 is provided with a branch line 41 for drawing distillate from receiving drum [8 for introduction to the reforming coil 45. A naphtha or gasoline fraction is withdrawn from the tertiary fractionating tower 23 of the viscosity-breaking unit by means of a line 48 and pump 48 and charged to the heating coil 45. A branch line 58 extends to receiving drum 25 for withdrawing distillate for introduction to the heating coil 45. A transfer line conducts the products from the naphtha reforming coil 45 to the separator 33.

The separated vapors from the evaporator 83 pass to a primary fractionating tower 52 and a secondary fractionating tower 53, the overhead vapors from which are condensed in condensing coil 54, discharging into a distillate receiver or gas separator 55. Primary reflux condensate is withdrawn from tower 52 by means of line 58 and pump 51 and conducted to the recycling cracking coil 28. Secondary reflux condensate is withdrawn from tower 53 by means of line 58 and pump 59 and conducted to the recycling cracking coil 35.

In one method of practicing the invention the single-pass reforming coil 45 is not employed and in this method of operation the charging stock introduced to the light gas oil cracking or vapor phase cracking coil 35 may advantageously contain gasoline constituents which it is desired to reform. For this operation-:ross-ove'r line 80 is provided so that gasoline fractions from trapout tray l4, as well as distillate from receiving drum i6, may be added to the fractions withdrawn from trap-out tray I3 for introduction into the cracking coil 36. If desired, instead of making the two cuts at trap-out trays l3 and I4, a single cut comprising light gas oil and gasoline constituents may be withdrawn from the tower ii for introduction to the cracking coil 36. For adding gasoline stock to the charge introduced by pump 39 to the cracking coil 38, a cross-over line 8i is provided. In this way the relatively low anti-knock naphtha or gasoline products produced in the viscosity-breaking operation may be combined with the light viscosity-breaker gas oil. Thus the gasoline or naphtha condensate collected at the bottom of tower 23, as well as light distillate collected in receiving drum 25, may be introduced into the cracking coil 38. If desired, the tower 28 may be dispensed with and a single cut withdrawn from tower 22 containing gas oil and gasoline constituents directed into the cracking coil 38.

In a modification of the invention the naphtha reforming coil 45 is employed to subject to reforming the gasoline constituents separated from the crude oil charge, and also, if desired, the gasoline constituents separated from the viscositybroken products. In this method of operation the reduced crude is subjected to viscosity-breaking in cracking coil l8, primary reflux condensate from trap-out tray I2 of tower Ii and primary reflux condensate from tower 2| is subjected to cracking in heating coil 28, secondary reflux condensate from trap-out tray l3 of tower H and secondary reflux condensate from tower 22 is subjected to cracking in vapor phase cracking coil 35, and gasoline or naphtha fractions, as withdrawn from trap-out tray ll of tower II, or gasoline or naphtha distillate from receiver i5, is subjected to reforming conditions in cracking coil 45; and gasoline or naphtha fractions produced in the viscosity-breaking operation, as withdrawn from tower 23 or from receiver 25. may also be subjected to reforming in cracking coil 25. The heavy gas oil cracking coil 28 and the light gas oil cracking coil 38 are-operated under recycling conditions. primary reflux condensate from tower 52 being cycled to cracking coil 28 and secondary reflux condensate from tower 58 being cycled to cracking coil 38. The

viscosity-breaking coil i8 is operated under single-pass conditions, the condensates formed in tower 2| and- 22 being directed to cracking coil 28 and 38 respectively. The naphtha reforming coil 45 is likewise operated under single-pass cracking conditions.

In practicing the invention the reduced crude is subjected to temperatures approximating 860 925' F. ,inthe viscosity-breaking coil l8 under conditions to effect about 10 percent of cracking per passas measured by conversion into 400 F. endpoint gasoline. Under these conditions there is a relatively large conversion into intermediate constituents of the nature of gas oil, particularly light gas oil constituents. The viscosity-breaking operation is advantageously carried on under pressures of about 100-200 pounds. The cracking of the heavy gas oil con stituents in the recycling cracking coil 28 is carried on at temperatures of about 9004000 F. but under a limitation as to the time of reaction so as to effect about 15 percent cracking per pass. The pressures employed in the cracking coil 28 are preferably about 300400 pounds, although higher pressures even up to as high as 1000 pounds may be used. Cracking in the cracking coil 38 is carried on at temperatures of about 9004000 F. with conditions of 20 to percent cracking per pass and under pressures preferably of about 200-400 pounds pressure. When not using the naphtha reforming coil 45, and when the charge to the cracking coil 38 includes material quantities of gasoline constituents, the cracktration, it should be understood that various modifications and adaptations thereof which will be obvious to one skilled in the art, may be made within the spirit and scope of the invention gasoline constituents, subjecting said liquid residue to single-pass cracking in a viscositybreaking zone wherein the liquid residue is sub-.

jected to cracking temperature under viscositybreaking conditions to effect conversion into a relatively large yield of intermediate constituents and a smaller yield of gasoline constituents, pass- 1 ing the resultant viscosity-broken products into a first separating zone wherein vapors separate from residue, fra'ctionating the separated vapors in a, first fractionating zone to form a heavy reflux condensate, an intermediate reflux condensate and a lighter fraction containing gasoll line constituents, combining said heavy condensate with'said heavy reflux condensate and subjecting the combined oils to cracking conditions of temperature and pressure in a first recycling cracking zone, combining said intermediate condensate with said intermediate refiux condensate and subjecting" the combined oils to cracking conditions of temperature and pressure in a second recycling cracking zone, combining said lighter fractions containing gasoline constituents and subjecting the fractions thus combined to single-pass cracking in a oncethrough reforming zone wherein the gasoline constituents are subjected to cracking conditions of temperature and pressure adequate to efiect reforming of gasoline constituents into com ponents of increased anti-knock value, passing the resultant cracked products from both of said recycling cracking zones and from said oncethrough reforming zone into a common separating zone, separate from said first separating zone, wherein vapors separate from residue, fractionating the separated vapors in a second fractionating zone to form a heavier cycle condensate, an intermediate cycle condensate and a final gasoline distillate, directing said heavier cycle condensate to said first recycling cracking zone, and directing said intermediate cycle condensate to said'second recycling cracking zone.

-2.' In the cracking of hydrocarbon oils, the process that comprises subjecting crude petroleum to fractional distillation to form a liquid residue, a heavy condensate, an intermediate condensate and a lighter fraction containing gasoline constituents, subjecting said liquid residue to single-pass cracking in a viscosity-breaking zone wherein the liquid residue is subjected to cracking temperatureunder viscosity-breakingconditions to eifect conversion into a relatively large yield of intermediate constituents and a smaller yield of gasoline constituents, passing the resultant viscosity-broken products into a separating zone wherein vapors separate from residue, fractionating the separated vapors in a first fractionating zone to form a heavy reflux condensate and a lighter condensate, combining said heavy condensate with said heavy reflux condensate and, subjecting the combined oils to cracking conditions of temperature and pressure in a first recycling cracking zone, combining said intermediate condensate from the fractional distillation of the crude petroleum with said lighter condensate from the viscosity-broken products and subjecting the combined oils to cracking conditions of temperature and pressure in a \second recycling cracking zone, subjecting said lighter fraction containing gasoline constituents to single-pass cracking in a once-through re-' forming zone wherein the gasoline constituents are subjected to cracking conditions of temperature and pressure adequate to effect reforming of gasoline constituents into components of increased anti-knock value, separating the resultant cracked products from both of said recycling cracking zones and from' said oncethrough reformingzone into vapors and residue,

fractionating the separated vapors in a second

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