US2193776A - Conversion of hydrocarbon oils - Google Patents

Description

March 12, 1940.

R. F. yTr-:ow

CONVERSION OFHYDROCARBOIN OILS' Filed sept. 19, 195s i Patented Mar. 12, 1940 PATENT GFFQE CONVERSION OF HYDROCARBON OILS Richard F. Trow, Tuckahoe, N. Y., assignor, by mesne assignments, to Texaco Development Gorporation,New York, N. Y., a corporation of Delaware Application September 19, 1938, Serial No. 230,539

4 Claims.

This inventionrelates to the conversion of hydrocarbon oils and has to do more particularly with a combination crude distillation and cracking unit utilizing the principle of gas reversion.

It is an object of the inventionr to segregate the virgin and cyclic or refractory stocks and toy convert the refractory stocks in the presence of nor mally gaseous hydrocarbons to obtain gas reversion. l

In accordance with the invention, a suitable charging stock such as crude petroleum is sub jected to distillation to obtain products, including straight run gasoline, kerosene, virgin gas oil and crude residuum. The virgin gas oil is subjected to independently controlled conversion conditions to obtain the desired conversion into gasoline, normally gaseous hydrocarbons, cracked gas oil and cracked residuum. The cracked residuumis ash distilled to produce a cycle gas oil which is combined with the crude residuum and the mixture of crude residuum and cycle gas oil,'and the cracked gas oil, are each subjected to independently controlled conversion conditions in the presence of normally gaseous hydrocarbons to effeet conversion of the oils and gases into lower boiling products, such as gasoline.

AA virgin cracking stock may be successfully converted and optimum conditions of time, .ternperature and pressure conveniently obtained in the absence of added normally gaseous hydrocarbons, ordinarily employed in gas reversion. On the other hand, it has been found that gas reversion may be more advantageously employed in the conversion of the cyclic or refractory stocks, wherein time, pressure and temperature conditions Optimum for conversion are more diflicult to obtain Without excessive tar and coke formation.

The cracking of a mixture of crude residuum, cyclegas oil, and normally gaseous hydrocarbons is advantageous because the latter two components serve as refractory diluents and permit the maximum conversion of the less refractory crude residuum without exceeding ther maximum f allowable overall crack per pass.` The presence of the normally gaseous hydrocarbons has another effect in that the hydrocarbons yenter the reaction to produce a higher gasoline yield and minimize the formation of cyclic tars. The presence of the normally gaseous hydrocarbons also contributes toward ease in control of the proper degree of vaporization` without the necessity of maintaining excessively high temperature levels.

The invention will be more fully understood from the following description read in connection with the accompanying drawing which shows a diagrammatic sketch of one form of apparatus for carrying out the process of the invention.

A charging stock, such as crude petroleum, is introduced through the line i and forced by the pump 2 through a heating coil 3 wherein the oil is preheated to sufficient temperature to eifect distillation of gasoline, kerosene and a major portion of the gas oil. The preheated oil is passed through line 4 to the lower portion of fractionator ,5 which is maintained under atmospheric pressure. Vapors separating in the fractionator pass upward .therethrough and are fractionated, the uncondensed vapors of straight run gasoline passing out from the top of the fractionator through the line 8, the kerosene condensing to form a side stream which is drawn off through the line 5, and a light gas oil fraction collecting on the tray The crude residuum remaining in the lower portion of the fractionator 5 is withdrawn through the line l2 and forced by the pump l t through a heating coil l5 wherein the residuum is further preheated under Vacuum and the hot products transferred through the` line IB to an l is withdrawnby the pump 25 through the line which merges with-the line 23, whereby the gas oils, both from the atmospheric tower 5 and the vacuum tower l1 are combined and pass through the line 28 to a preheater coil3ll located in an evaporator 3 I, referred to hereinafter. The pre* heated virgin gas oil is then passed through the line 32 to a heating coil 35 wherein it is raised to a cracking temperature of about 900 to 1900o F. and the hot products then transferred through the line 36 to a soaker 38, which is maintained under a pressure of about 750 pounds per square inch. The products pass upwardly through the soaker 3S wherein conversion takes place and the cracked products are thereafter transferred through the line 40 to the evaporator 3l. The evaporator 3l is maintained under a pressure, for example about 200 to 250 pounds per square inch.

In the evaporator 3l the cracked products separate into vapors and residuum, the vapors passn ing overhead through vaporline 42 to a fractionator 45. ln the fractionator 45 hydrocarbons of higher boiling point than the desired gasoline are condensed to form a reflux condensate or recycle stock which collects in the lower poltion of the fractionator from which it is withdrawn by the pump G6 and forced through the line 50 to a recycle or cracked gas oil heater 50. In the heater 50 the clean cracked gas oil is heated to a temperature of around 900 to l100 F. and the hot products then transferred through the line 5| to a soaker 52 which is maintained under a pressure of about 250 pounds per square inch, or higher, wherein sucient time is provided for conversion to taire place. The cracked products are then 'transferred through the lines 55 and d0 to the evaporator 3E.

The cracked residuum is withdrawn from the lower portion of the evaporator 3| and passed through the line 55 to the lower portion of the taz' stripper 55. The tar stripper is maintained under reduced pressure, for example atmospheric or slightly above, for example 15 pounds or less. The residuum is fiash distilled in the tar stripper ie vapors of the more Volatile constituents s into the upper portion of the tar stripper, wherein the heavier vapors are condensed to produce a cycle gas oil which collects on the tray The uncondensed vapors pass overhead from the tower 55 through the vapor line 60 and condenser to a receiver G2, wherein a gasoline fraction is collected. A heavy cracked fuel oil is withdrawn from the bottom of the tar stripper 5S through the line 60.

The heavy crude bottoms collecting in the lower portion oi the vacuum tower Il are withdrawn therefrom through the line 58 in which is located a pump T0. Any portion or all of the bottoms may be passed through the branch line 'll and introduced into the upper portion of the tar stripper 5t through either or both of the manifold lines 'i3 and 14, If desired, any portion or all of the heavy crude bottoms may be passed through the branch line l5. The cycle oil is withdrawn from the tar stripper 55 irough the line l0 and in mixture with the crude bottoms, discharged through the branch line il or the branch line 15, forced by the pump through the line '19 to a heating coil 80, wherein the oil. is raised to a cracking temperature of about 850 to 1000* F. and the hot products transferred through the line 8| to the scalrer 52.

The gasoline fraction collected in the receiver is withdrawn therefrom by the pump 83 and passed through the line 84 to the fractionator 45, wherein the gasoline is introduced at the desired level through branch lines 85 or 35, to serve as a reflux medium. A portion of the gasoline frein the line 34 may be passed through the i branch line 8l to the upper portion of the tar passed through the branch line 93 and line B5 to the upper portion of fractionator 45 as a reflux medium. The remainder of the unstable cracked gasoline is conducted through the line '.lfi to a stabilizer 95, wherein stabilization takes 7,3 place, and a stabilized gasoline is withdrawn from the lower portion of the stabilizer through the line 90. The stabilizer overhead, comprising principally C3 and C4 hydrocarbons, is withdrawn from the upper portion of the stabilizer through the line 90 and condenser 99 to a receiver |00. A portion of the stabilizer overhead is recycled by the pump E02 through the line |03 to the upper portion of the stabilizer 95 as a reflux medium. The remainder of the stabilizer overhead is forced through the line |05 and introduced into either heater coil 80 or the heater coil 50, or both, through the branch lines |06 and ll. The stabilizer overhead so introduced into the heaters is converted into normally liquid hydrocarbons in admixture with the oil undergoing cracking therein.

The uncondensed gases and vapors in the receiver 90 are passed through the line |09 to an absorber Ht which may be operated under a pressure of about 200 pounds. Also normally gaseous hydrocarbons from the receiver 62 are passed through the line H2 by the pump H3 to the absorber 0. Any portion or all of the heavy recycle gas oil withdrawn from the tray 58 of the tar stripper 55 may be passed through the line i3, pump 'I3 and line H5 to the upper porltion of the absorber ||0 to act as an absorption medium. The absorption medium may contain any portion or all of the heavy crude bottoms withdrawn from evaporator |l through the lines 5G and ll. It is preferable to pass the heavy crude bottoms directly through the lines 68, and '1.9, directly to the heating coil 80 and use only the recycle gas oil collecting on the tray 56 of the tar stripper 55 as an absorption medium in the absorber H0. In the absorber the gas oil scrubs out the heavier constituents, such as hydrocarbons between 2 and 5 carbon atoms, from the gases, thereby becoming enriched. The unabsorbed gases are released from the top of the absorber by the line while the enriched absorbent oil is withdrawn from the bottom of the absorber by the pump ||8 and forced through the line H0 to the preheating coil |20, located in the upper portion of the fractionator 45 and thence through the line |2| to the heating coil S0. The normally gaseous hydrocarbons absorbed in the cycle gas oil undergo conversion in the presence of the normally liquid hydrocarbons in the conversion operation.

Ordinarily the process herein described is selfcontained, that is, suiicient normally gaseous hydrocarbons are produced in the system to effect the desired gas reversion. However, in case additional normally gaseous hydrocarbons are desired, a further supply of hydrocarbons, such as propane, butane, or a mixture of propane and butane, may be introduced through the line |24 and pump |25.

As an example of the operation of the invention, an East Texas crude petroleum is preheated to a temperature of about 600 F. and subjected to atmospheric distillation to remove the straight run gasoline, kerosene and virgin gas oil. The products are further distilled under Vacuum to separate an additional quantity of virgin gas oil leaving fuel oil bottoms of about 17 A. P. I. gravity. The combined virgin gas oils, having a gravity of about 32 A. P. I. are heated to a temperature of about 930 F. and subjected to conversion in a soalrer under a pressure of about 750 pounds per square inch. The reaction products are introduced into an evaporator operating under a pressure of about 230 pounds per square inch, whereinv separation between vapors and pressure tar occurs. The vapors are fractionated to produce a clean recycle stock which is heated to a temperature of about 960 F. and introduced into a soaker which is maintained under a temperature of about 910 F. and a pressure of about 250 pounds. The cracked products from the soaker are passed into the evaporator mentioned above. The pressure tar is subjected to flash distillation to produce a tar stripper or cycle gas oil of about 20 A.,P. I. gravity Which is used as an absorption medium for absorbing the heavier constituents of the normally gaseous hydrocarbons produced in the system. A mixture of the enriched cycle gas oil and heavy crudeA bottoms of about 17 A. P. I. gravity, referred'to heretofore, is heated to about 900 F. in a black oil heater and the hot products discharged into the aforementioned soaker, receiving the products from the clean oil heater. An unstable cracked gasoline is recovered and subjected to stabilization and the stabilizer reux is introduced into the black oil and clean oil heaters. The normally gaseous hydrocarbons introduced into these heaters amount to about 68% of the total charge to the heaters. A yield of gasoline, based on the crude, of about with an octane number of about 70 is obtained.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.- i

I claim:

1. A process for the conversion of hydrocarbon oils which comprises ,distilling a crude petroleum in the absence of substantially any cracked products to produce a reduced crude and virgin gas oil, subjecting said virgin gas oil substantially free from refractory cracked materials to a once-through cracking operation, separating the cracked products into vapors and residuum, flash distilling the residuum to produce a cycle gas oil, subjecting a mixture of said cycle gas oil and said reduced crude to separate cracking in the presence of normally gaseous hydrocarbons under reversion conditions in a coil and soaker, separating the cracked products from the soaker into vapors and residuum, subjecting the last mentioned residuum to the flash distillation operation in Which said first mentioned residuum is flash distilled, fractionating the vapors from both of said cracking operations to recover a clean recycle stock, subjecting said recycle stock to cracking in a separate coil, discharging the cracked products from the last mentioned coil into said soaker to undergo soaking together with the cracked mixture of said crude residuum, cycle gas oil and normally gaseous hydrocarbons, and recovering gasoline from the system.

2. A process according to claim 1 in which the cracked products from the virgin gas oil cracking operation and the cracked products from said soaking operation are passed to a common separator.

3. A process according to claim 1 in which the clean recycle stock lis cracked both in the coil and in the soaker in the presence of normally gaseous hydrocarbons under gas reversion conditions.

4. A process according to claim 1 in which u cracked gases from the system are scrubbed with the cycle gas oil and the enriched cycle gas oil treated in the gas reversion operation. RICHARD F- TROW,

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