US2130988A - Treatment of hydrocarbon oils - Google Patents

Description

Sept. 20, 1938. J. K. ROBERTS TREATMENT OF HYDROCARBON OILS Original Filed July 27, 1933 INVENTOR C I .Q/

ATTORN EY Patented Sept. 20, 1938 UNITED ,STATES' 2,130,988 mammor mmnocmnon on.s

Joseph K. Roberts, Hammond, ma, assignor to Standard.- Oil Company (Indiana), Chicago, 111., a corporationoi' Indiana Application July 27, 1933, Serial No. 682,458

I RenewedDecember 6, 1985 10 Claims. (Cl. 1196-94) This invention relates to the pyrolytic treatment of hydrocarbon oil for the purpose of converting the same into oils of lower boilingpoint,

such as gasoline or naphtha, and has an especial relation to the recovery of the low-boiling oil resulting from such pyrolytic conversion.

' An object of my invention is to provide a process for converting hydrocarbon oil to lower-boiling oil having improvements with respect to prior processes, especially with respect to the recovery of the lower-boiling oils produced therein and with respect to the utilization of available heat in the process.

My invention has for a further object the provision of a process for fractionating mixed hydrocarbon vapors resulting from the pyrolysis or cracking of hydrocarbon oils wherein the separation and removal of the various products therefrom in the desired form may be facilitated.

I My invention has for further objects such additional improvements in operative advantages and results as may hereinafter be found to obtain.

As is well known, when petroleum oils are i cracked for the production of lower boiling oils, the vapors resulting from the cracking operation contain, besides residual constituents which are removed while the oil is still at a cracking temperature or before it has cooled to temperatures that may be said to be within a condensing range, constituents heavier than gasoline, such as gas oil, gasoline constituentsand lighter constituents, including incondensible gases and very light hydrocarbon materials, the presence of 5 which is undesirable in the final gasoline product due to their high volatility. In-cooling these vapors prior to removal of the gasoline condensate, that is to say, in fractionating these vapors for the removal of constituents heavier than gasoline, a considerable amount of cooling is necessary, or, stated differently, a considerable excess of heat is available, At the same time, however, the quantity of reflux passing through the rectifying or fractionating operation, can not ordinarily be materially lessened by the withdrawal of material amounts of reflux liquid from the system for the purpose of utilizing the heat of such reflux elsewhere in the system, without disadvantage, as for example, by seriously interfering with the proper balance of conditions in the cracking and fractionating operations;

v If an amount of the hot reflux liquid available within the fractionating tower sufficient to effect the desired rebelling of the light distillate in the 5 stabilizing operation is withdrawn for-such pur- .heat to the incoming fresh charge.

pose and then removed fromthe system, not only does this mean that the fractionating tower is deprived of a certain amount of the cooling necessarily effected therein but the amount of recycle stock available for cracking is decreased. 5 My invention therefore contemplates, in a ,process for cracking hydrocarbon oil, suchas gas oil or reduced crude or a mixture thereof, the delivery of mixed cracked vapors containing gasoline constituents, constituents heavier than gasoline and constituents'lighter than gasoline, into a fractionatingzone wherein products heavier than gasoline, such for example as gas oil or other oil suitable for further cracking, are separated from the vapors, condensing the remaining vapors to recover a gasoline distillate, and delivering the gasoline distillate to a stabilizing or fractionating zone wherein the gasoline distillate or condensate thereby obtained is stabilized to produce the desired motor fuel product, the heet employed in the stabilizing zone being derived from products heavier than gasoline removed from the first fractionating zone.

My invention'further contemplates, as an important and novel aspect thereof, returning the condensate heavier than gasoline, after indirect heat exchange with the relatively light distillate passing through the stabilizing zone and preferably without further cooling. thereof, to the stream of vapors at some point between the v point of liberation thereof in the cracking system and the point where the gasoline-vapors are removed from the fractionating zone. More specifically, this oil heavier than gasoline, after such heat exchange, may be returned to the first fractionati'ng zone, preferably at a point above the point of introduction of vapors thereto, or to some point prior thereto along the flow of-the vapors liberated in the cracking operation.

My invention further contemplates, where de- 40 sired, the withdrawal ofan additional stream of condensate heavier than gasoline from the fractionating zone for the purpose of being admixed with the partially cooled oil after passage through the reboiler or stabilizing zone and before being returned to the vapors passing through or about to pass through the fractionating zone. In the preferred instance, this second stream of oil may be employed for the purpose of imparting According 5 to this feature of my invention it is possible to control therefluxing within the fractionating zone in a highly advantageous manner,due to thefact that either the temperature or amount of the oil withdrawn from the fractionating zone and ultimately erence 'to the drawing accompanying and forming a part of this specification, a preferred manner in which my invention may be practiced and embodied, but without limiting my invention to such illustrative exempliflcation or embodiment in this drawing. i

The single figure is a more or less diagrammatic elevational view or flow diagram of a plant or system for cracking hydrocarbon oil, embodying the various features of my invention.

Referring now to the drawing, the apparatus comprising the plant or system includes principally a furnace I, provided with a heating or cracking coil, .a reaction chamber 2, an evaporator or separator 3, a flash chamber 4 adapted to receive liquid from the evaporator 3, a fractionator or bubble column 5 and a fractionator or stabilizer 6, together with various appurtenances such as conduits, valves, pumps, heat exchangers, coolers, gas separators and the like, to be described more fully herebelow.

- In the instance illustrated, the apparatus has been designed with a view to handling a gas oil stock, such for example as gas oil from Wyoming crude. It will be understood by those skilled in the art, however, that my invention in its broad aspect is not limited to the charging of any particular stock nor to the particular manner or' apparatus in which the cracking is effected.

In the present instance, however, a charging stock, which may comprise agas oil, is delivered by means of a pump II from a source (not shown) to a conduit i2 having a valve l3 into the interior of the fractionating column 5 at a point preferably about midway of the height thereof. In passing through the conduit l2 the charge oil passes through heat exchangers I4 and I5, to be described more fully hereinbelow,

. wherein its temperature is raised to a point preferably approximately or a little lower than the temperature within the iractionating column 5 at the point of introduction of the charge oil.

The fractionating column 5, through, a vapor line [6, receives mixed hydrocarbon vapors resulting from the cracking of hydrocarbon oil and from which residual or dirty constituents have previously been removed. These vapors enter the .lower portion of the tower 5 and pass upward therethrough, and as the result of cooling effected by means of relatively cool oil introduced through the conduit l2 and/or conduits l1 and I8, a condensing and rectifying efiect is obtained, this condensation-and rectification being so controlled as to remove and condense from the vapors con stituents heavier than gasoline, which pass downward through the tower and ultimately collect in the bottom of the tower, a portion of which may be withdrawn by means of one or more trapout trays such as those illustrated at i9, 20, and 2|. It willbe obvious to those skilled in the art that the temperature and composition of the material withdrawn from any of the aforesaid trapout trays will depend upon the location of the trapout tray with. respect to the remaining portions of the column and also with respect to the temperature at the point of withdrawal, as well as the relation of the particular trapout tray In any event, however, a condensate or reflux heavier than gasoline, and ordinarily comprising a clean gas oil suitable for cracking at relatively high temperatures, collects in the bottom of the fractionating column 5 and is withdrawn therefrom through a conduit 23- having a valve 24, to be delivered by a pump 25 to the cracking furnace I. The oil thus withdrawn from the bottom of the fractionating column 5 ordinarily has a temperature oifrom 550 F. to 700 F., and inpassing through the coils located within the furnace I, which maybe of any suitable construction, is heated to a suitable cracking temperature of, for example, 850 F. to 1050" F., under a pressure of as high as 1000 pounds per square inch or even higher; In a preferred instance the gas oil is withdrawn from the base of the fractionating column 5 at a temperature of about 680 F. and is heated to a temperature'of from about 900 to about 925 F. while traversing the furnace I.

The extent of cracking effected while the oil is traversing the furnace I will vary, of course, with the nature of the results desired and the nature of the charging stock, but is ordinarily carried as far as possible without undue deposition of carbon or coke within the coils of the furnace. In a typical instance, however, the conditions of time of contact and temperature are soregulated as to produce a crack per pass of approximately 20%.

The resultant hot cracked products pass from the coil in the furnace I through a transfer line 26 to a reaction chamber 2, which, in the instance illustrated, comprises a chamber of the wellknown Cross type which is adapted to be maintained at a pressure of from 500 to 1000 pounds per square inch, and preferably 750 pounds per .square inch. The hot vaporousproducts passing through the reaction chamber 2 undergo digestion and further cracking, and the resultant products are discharged therefrom through a conduit 21, having valves 28 and 29, into an evaporator or separator 3 maintained at materially lower pressure, for example, from 25 to 300 pounds per square inch, and preferably about 200 pounds per square inch. The interior of the evaporator 3 may be provided with suitable fractionating plates or trays 3i and 32 and also with baflles 33, the choice and, disposition of such conventional elements being a matter of specific design in each specific instance and not necessary to be described in further detail.

Within the evaporator 3, under the influence of the reduction of pressure which takes place light constituents of the liquid removed from the evaporator 3 are volatilized and pass out as vapors through a conduit 36 leading to the heat exchanger I4 where they are partially cooled by exchanger or condenser 31 and the condensatev passes to a separator 38, from which any gases are removed through a valved conduit 39, while indirect heat exchange with the fresh charging oil passing through the conduit l2.

The vapors are then further cooled in a heat the condensed flash distillate is removed through a conduit 4| having a. pump 42. A portion of this flash distillate may be returned through a branch conduit 43 having valves 44 and 45 to the upper portion of the flash chamber 4 to serve as reflux therein, while the remainder or excess of the flash distillate passes through a branch conduit '46 having a valve 41 and in which is located heat exchangers 48 and 49, to be introduced into the evaporator 3 either through a valved inlet 51 located about midway of the height of the evaporator 3 or a valved inlet 52 located near the top of the evaporator 3 or both. In this manner all of the excess flash distillate over and above that returned to the flash chamber 4 as reflux is delivered to the evaporator 3 for further distillation therein and for the purpose of acting as a reflux and cooling agent in the evaporator 3. 1

The partially cooled and dephlegmated vapors leave the top of the evaporator at a temperature of, for example, from 650 F. to 800 F. and-pass to the fractionating column 'for further dephlegmation and fractionation in the manner already described.

Residual portions of the flashed liquid which are not volatilizejd in the flash chamber 4 collect in the bottom'of the latter and are withdrawn through a conduit 54 having a valve 55 and leading to the heat exchanger 49, wherein the liquid or fuel oil thus withdrawn is caused to and comprising constituents not heavier than gasoline, pass out of the fractionating column 5 through a conduit 51 and pass successively through a heat exchanger 53, the heat exchanger 48 and a condenser 59, the resultant mixture of vapors and condensate passing into a separator 60. From theseparator 60 incondensible gases are removed through a valved conduit 6|, while :the gasoline condensate is withdrawn through or required as reflux in the column 5 passes from the conduit 53 through a conduit 52, wherein is located a valve 65 and the heat exchanger 58 and is thendelivered through one or more valved inlets 65,- 51 into the stabilizing column 6. A valved by-pass line 58' is provided for controlling the action of heat exchanger 58.

It will thus be seen that the gasoline vapors passlngoutjof the column S'flrst pass in indirect heat-exchange relationship in the heat exchanger 58 with-the condensate obtained therefrom, and then in indirect heat-exchange relationship in the heat exchanger 48 with flash distillate removed from the separator 38 and about to be returned to the evaporator 3.

Within the stabilizing column 6 the preheated gasoline, which has been brought to a temperature of from 250 to 400 F., and preferably about 315 F., is subjected to a reflux distillation and fractionation effectfor the removal of constituents lighter than those desired in the final gasoline motor fuel product. The liberated vapors reaching the top of the stabilizing column B, which is preferably maintained at a pressure of, for example, from '25 to 300 pounds per square inch, and in a typical operating instance at 250 pounds per square inch, pass out of the stabilizing column 6 through a vapor line H to a condenser 12 from which the mixture of condensate and vapors then passes to a separator 13. Incondensible gases are removed fromthe latter through a valved conduit 14. The condensate collecting in the separator 13 is all returned v through a conduit 15 having a pump 16 to the ed to a temperature of, for example, from 150 F. to 425 F. In this manner, a reboiling and complete stabilization of the gasoline is obtained, the final stabilized product passing out through the stabilizing column 6 through a valved outlet 82.

In order to supply heat to the reboiler or heat exchanger 15, condensate heavier than gasoline and representing a considerable portion of the available reflux liquid within the column 5 is withdrawn from the bottom of the fractionating column 5 and/or fromany of the trapout trays I9, 20, or 2|, and passes through a conduit 83 to a pump 84. A portion or all of this liquid is then passed through a branch conduit 85'having the valves 86 and 81 through the heat exhanger or reboiler 15 where it passes in indirect heat-exchange relationship with the gasoline being stabilized in the column 6, and the partially cooled liquid then returns, without further cooling, through a conduit 88 having a valve 89 for delivery to the stream of vapors at some point between the reaction chamber 2 and the top of the fractionating column 5.

A valved by-pass line 89' is provided for ad- ,J'usting the flow through the heat exchanger 19.

A further stream. of .reflux is preferably withdrawn from the fractionating column 5 and is passed through a branch conduit 90 having a valve 9| to the heat exchanger I5 where it passes in indirect heat-exchange relationship with the fresh charge. A valved by-pass 90 is preferably located in the line 50 for the purpose of adjusting the flow through the heat exchanger l5 and, if desired, for the purpose of byf-passing the heat exchanger l5 entirely. Ordinarily, however, a portion of the oil is passed through the heat exchanger l5 and the streams of oil passing through the conduits 8 8 and 90 are then combined and pass, either through the valved inlet l1 into the interior of the'fractionating column 5, or through a valved conduit 92 which communicates with the conduit It at a point just above the top of the evaporator 3. It will be understood, however,

that the cooled oil withdrawn from the column to introduce it at a point located above the point of introduction of vapors into the latter.

While, as I have stated hereinabove, the temperature of the oil thus withdrawn from the col-v umn 5 will vary considerably according to the point of withdrawal and other factors, in a typical operating instance, a gas oil condensate or reflux is withdrawn from the trapout tray II at a temperature of about 680 F. and is utilized in bringing the fresh charge passing through the heat exchanger 15 to a temperature of about 420 F. prior to its entry into the fractionating column 5, and also to maintain a temperature of approximately 395F. in the base of the stabilizing column 6, before being returned at a temperature ranging from 400 to 450 F. to the interior of the fractionating column 5.

By means of my invention the excess.lheat available within the fractionating column 5 may very efficiently be utilized without unduly disturbing the refluxing conditions within the column 5. Conversely, a proper degree of cooling may readily be obtained within the column 5 without loss of an equivalent amount of heat to the system. c

By regulating the valves 86, 9| and the valve by-pass 89', it is possible to adjust the proportion of the oil withdrawn from the fractionating column 5 and delivered to the heat exchanger M or the heat exchanger 19, respectively, in such manner that either the temperature. or the amount of the oil thus withdrawn and returned to the vapors as a-refiux may be independently regulated. These advantages are obtained without requiring additional cooling which would result in a loss of heat to the system as a whole.

While I have described my invention hereinabove with reference to a more or less specific and preferred embodiment and with respect to a particular type of cracking system, it may be employed with advantage in other types of crack ing systems, without reference to the specific temperatures or pressures set forth herein. My invention is not, therefore, limited to the specific "details whiclfhawe been' set fiirth' hereinabove by way of example, but may variously be practiced and embodied within the scope of the claims hereinafter made.

I claim:

. 1; The process of obtaining stabilized gasoline from relatively high boiling hydrocarbon oil which comprises charging said oil into a fractionating zone receiving hot cracked vapors, recovering a fraction consisting of constituents heavier than gasoline from said zone, passing a stream of said fraction through a heating zoneand heating it while in transit therethrough to acracking temperature, dephlegmating the resultant cracked products ,to produce the aforesaid hot cracked vapors, removing vapors containing gasoline from said fractionating zone,

condensing them to recover a gasoline fraction therefrom, removing a stream of hot reflux lighter than said fraction first mentioned and'com prising constituents heavier than gasoline, from said fractionating zone, passing said stream of reflux in heat exchange relationship withthe fresh oil about tobe charged into said fractionating zone, thereby preheating said charge oil by means of excess heat in said reflux, and return? ing said reflux to said fractionating zone, passing another portion of the reflux'formed in said fractionating zone in indirect heat exchange relation with gasoline fractions formed by condensation of vapors removed from said fractionating zone, to cause partial vaporization of said gasoline fractions, returning resulting cooled reflux to said fractionating zone and removing the unvaporized portions of said gasoline fraction as a desired product.

2.' The process of producing stabilized gasoline distillate from mixed hydrocarbon vapors containing gasoline constituents, constituents heavier than gasoline, and constituents lighter than gasoline, which comprises delivering said vapors to a fractionating zone wherein constituentsheavier :than gasoline are condensed, withdrawing the remaining vapors and cooling them to condense gasoline constituents, subjecting the gasoline condensate thereby obtained to reflux distillation under superatmospheric pressure under the influence of indirect heat exchange with relatively hot constituents heavier than gasoline withdrawn from said fractionating zone, combining said constituents heavier than gasoline after such heat exchange with a further stream of oil comprising constituents heavier than gasoline, said further stream of oil consisting. of reflux condensate withdrawn from said fractionating zone and cooled separately fromsaid relatively hot constituents withdrawn from said fractionating zone, and returningv the combined stream of oil to the stream of vapors at a point prior to the removal of the uncondensed gasoline vapors from said'fractionating zone.

3. The process of producing stabilized gasoline distillate from mixed hydrocarbon vapors containing gasoline constituents, constituents heavier than gasoline, and constituents lighter than gasoline, which comprises delivering said vapors to a fractionating zone wherein constituents heavier than gasoline are condensed, withdrawing the remaining vapors and cooling them to condense gasoline constituents, separating uncondensed gases from resulting gasoline. distillate and subjecting the gasoline condensate thereby. obtained to reflux distillation undersuperatmospheric pressure in a separate fraction'ating zone under the influence of indirect heat exchange with relatively hot constituents heavier than gasoline withdrawn from said first mentioned fractionating zone, preheating fresh charging stock by indirect heat exchange with additional relatively hot constituents heavier than gasoline withdrawn from said first mentioned fractionating zone, introducing the preheated fresh charging stock into an intermediate point in said flrst mentioned fractionating zone, and returning said constituentsheavier than gasoline directly and substantially without further cooling after such heat exchange to said fractionating zone.

4. In a process for the fractional distillation of materials of relatively wide boiling range wherein heated vapors are subjected to fractionation in a first fractionating zone for the formation of condensate of a relatively high boiling nature and resulting fractionated overhead products subjected to further fractionation in a'sec- 0nd fractionating zone for the. separation of a relativelylow-boiling condensate from lower boiling constituents, the improvement which comprises subjecting said relatively low boiling condensate in said second fractionating zone to reboiling by'indirect contact and heat exchange 4 vapors in a first fractionating zone thereby iorming relatively heavy reflux condensate, further fractionating fractionated overhead products in a second .fractionating zone to separate a lighter reflux condensate, withdrawing heavy reflux condensate, from said first rractionating zone andpassing the same in indirect heat exchangerelation with said lighter condensate to reboil'the latter and thereby cooling the withdrawn heavy condensate, then returning such cooled heavy condensate to said first zone, and continuously supplying heavy reflux condensate from the first zone to the cracking step.

6. A conversion process which comprises cracking hydrocarbon oil, fractionating the resultant vapors in a first iractionating zone thereby forming relatively heavy reflux-condensate, further fractionatingfractionated overhead products in a second Iractionating zone to form a lighter reflux condensate, withdrawing heavy reflux condensate from said first zone and passing the same in indirect heat exchange relation with said lightercondensateto reboll'the latter and thereby cooling the withdrawn heavy condensate, then returning such cooled heavy condensate to said 7 first zone by commingling' the same with the vaporsentering this zone thereby to. decrease I the load in the latter, and continuously-supplying heavy reflux condensate from the first zone to the cracking step. 7

'7. A conversion process which comprises cracking hydrocarbon oil. fractionating the resultant 4o vapors in a first rractionatin'g zone thereby forming relatively heavy reflux condensate. further rractionating fractionated overhead products in condensate are returned to rurther conversion in 'thesamesystem.

a second iractionating zone to torm a lighter reflux condensate, continuously circulating heavy reflux condensate in a closed ring from said first zone through a cooling zone and then back to the first zone, passing the thus circulated heavy con-' densate, during its flow through said cooling zone,

in indirect heat exchange relation with said lighter condensate to reboil the latter, and continuously supplying heavy reflux condensate from the first zoneto the cracking step.

a. The process'as defined in claim '2 Iurther characterized in that the heavy condensate circulated in said ring is returned to the first fractionating zone by being commingled with the vapors entering this zone whereby to decrease the load of the first zone.

9. In a process for the conversion of hydrocarbonoils wherein an oil is subjected to conversion conditionsior elevated temperature and superat- 1 20 .mospheric pressure, the resulting'vaporous and non-'vaporous conversion products separated, va-

porous products soobt'ained subjected to free tionation in-a first fractionating zone .and a sec- :ond Iractionating zone whereby a higher-boiling fraction is condensed and separately collected in .said first iractionating zone and a relatively lowe'r-boiling fraction is separatedfrom lighter constitu'nts in said second iractionating zone; the improvement which comprises reboiling said low-' er-boiling fraction byindirect heat exchange fraction withdrawn from said first tractionating zone and returning'said regulated quantity of higher-boiling'traction; afterpassing in indirect heat exchange with saidllower-boiling fraction, to said first tractionating zone.-

30 .with a regulated quantity or the higher-boiling.

10. a processof the-character defined in claim 9 wherein high boiling fractions of the reflux scenes 1:. Ronr'mrs.

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