US2109875A - Process for the treatment of hydrocarbon oil - Google Patents

Description

March E, w3.. H. v. ATWELL PROCESS FOR THE IRE'IMENT OF' HYDROCARBON OIL Filed Deo. 31, 1955 Patented Mar. 1, 1938 PROCESS FOR THE TREATMENT OF HYDRO- CARBON OIL Harold v`. Arwen, white Plains, N. Y., assignmto Gasoline Products Company, Inc., Newark, N. J., a corporation of Delaware Application December 31, 1935, Serial No. 56,898

6 Claims.

This invention relates to processes for the cracking of hydrocarbon oils and pertains more particularly to a process for producing gasoline or other light hydrocarbons from relatively heavy oils which cannot ordinarily be economically and satisfactorily subjected to conventional coil cracking.

It is an object of my invention to provide a plural-coil cracking process wherein a plurality of clean distillate cracking stocks are subjected to conversion in separate cracking coils and a heavy stock, such as reduced crude, heavy distillate, or the like, is simultaneously subjected to a cracking operation in a reaction zone by aid of heat derived from one of the clean cracked stocks. v

More specifically, it is an object of my invention to provide a plural-stage cracking process wherein heavy oil, such as reduced crude, heavy distillate, or the like, is introduced into a cracking chamber or reaction zone and maintained therein at cracking temperature for a time sufcient to cause a considerable amount of conversion thereof, the resulting cracked products are introduced into an evaporator, residuum is removed from the evaporator, and likewise a side stream of heavy condensate, while the vapors are passed overhead to a fractionating zone wherein a nal desired distillate is removed as an overhead product and two condensate fractions are formed, one being a more or less conventional gas oil reflux condensate and the other a relatively lighter intermediate condensate. The former reflux condensate is passed to a separate cracking stage for additional conversion, while the latter reflux condensate, of a lighterv character, is passed through a separate cracking coil and subjected to a high cracking temperature, after which the cracked products are mixed with the reduced crude, heavy condensate, or other heavy charging stock for passage to the soaking chamber, the highly heated cracked light reux condensate constituting the source of heat for cracking the heavy charging stock. Simultaneously, if. desired, the heavy condensate withdrawn from the evaporator may be subjected to additional conversion in a separate stage.

A still further object of my invention is to provide a plural-stage cracking process wherein two cracking stages operating in the manner set forth in the preceding paragraph are utilized, the heavy cracked condensate from the first-mentioned evaporator passing to a second soaking drum or reaction zone for additional conversion and thence to a second evaporator, from which vapors are removed and fractionated to create additional redux condensate, preferably in two fractions, a -light fraction and a heavy fraction, the latter being passed to a separate stage for conversion, and the former, lighter fraction being cracked in a separate cracking coil at high temperature and utilized to heat the heavy stock introduced into the second soaking chamber.

Another feature of my invention contemplates the separate cracking of a clean stock such as Virgin gas oil and the introduction of the cracked products into the first-mentioned evaporator, and where two stages are utilized, the separate cracking of the heavy reflux condensate from the initial fractionating operation, and the introduction of the resulting cracked products into the second evaporator.

`'I'he above-mentioned and further objects and advantages of myiinvention and the manner of attaining them will .be more fully explained in the following description taken in conjunction with the accompanying drawing.

The single ligure of the drawing represents diagrammatically in side elevation and partly in section an apparatus adapted to carry out the process of my invention.

Referring more particularly to the drawing, fresh heavy charging stock, such as reduced crude, heavy distillate, fuel oil, or the like, is forced by pump I through conduit 2 into soaker `or reaction chamber 3, reaching there either directly through valved by-pass line 4 or heating -coil 5, located in furnace 6. In the soaker the heavy oil is maintained at a cracking temperature and subjected to conversion, as will be eX- plained more fully hereinafter, and the resulting cracked products are conducted through transfer line 'I having control valve 8 into the base of evaporator 9, wherein separation thereof into vapors and liquid residue takes place. The vapors pass upwardly through the tower around baffle trays or other fractionating elements Ill, thence through vapor line II into the base of fractionating column I2. In this column the vapors are subjected to fractional condensation in the usual way, the resulting reflux condensate being collected in two fractions, a heavier fraction, which is withdrawn from the base of the tower through draw-off line I3, and a lighter fraction, which is collected on trap-out tray I4, and withdrawn therefrom through pipe I5. This last-mentioned, lighter reflux condensate is forced by pump I 6 through heating coil Il of furnace 6 and is therein raised to a relatively high cracking temperature of, for example, 1000 to 1100c F., under a relatively high pressure of, for example, 500 to 1000 pounds per square inch, and is sub-jected to conversion. The resulting cracked products are conducted through transfer line i6 having control valve I9 into the soaker 3 in mixture with the heavy charging stock introduced thereinto through line 2, the relative quantities and temperatures of the heavy oil and lighter cracked reflux condensate being such that a temperature suicient to promote active cracking of the heavy oils is attained in the soaker, tiis temperature being, for example, in the range of 850 to 900 F. When the coil 5 is used to preheat the heavy charging stock, the amount of heat necessary to be supplied by way of heating coil I1 is naturally less than when the heavy charging stock is passed directly through line 4 to the soaker 3. Whether or not heating coil 5 is used the temperature to which the oil is raised therein will depend upon the character of the heavy oil to be cracked. When reduced crude is used, this oil may readily be raised to a cracking temperature and, if desired, be subjected to a considerable amount of conversion in the coil 5. But when exceedingly heavy or dirty stocks are used it will, in most instances, be desirable to utilize less drastic conditions in the coil 5, so that the oil is heated with relatively little or no cracking, or to avoid the use of the coil 5 at all, this being done by closing control valves 20 and 2l and opening valve 22. Because of the relative temperature to which the heavy oil and the lighter reiiux condensate are subjected, the coil 5 is most suitably located in the convection portion of the furnace, and the coil i1 in both the convection and radiant portions of the furnace, as shown on the drawing. The heavy charging stock and lighter cracked reflux condensate are shown as entering the soaker 3 through a common connecting pipe, but obviously separate connecting lines might be used for this purpose, if desired.

Simultaneously with the introduction of. heavy charging stock through line 2, a relatively clean charging stock, such as gas oil, is introduced to the system through conduit 23, being forced by pump 24 through heating coil 25 located in furnace 26. In this heating coil the oil is raised to a desired cracking temperature, for example, in the range of 900 to 1000 F. and is therein subjected to conversion, the resulting hot cracked products being passed through transfer line 21, having control valve 28, into the base of evaporator 9. Alternatively part or all of this highly heated stock may be conducted through pipe 29 having control valve 30 into the soaker 3 for further conversion therein in mixture with the heavy charging stock and lighter reflux condensate, and in this event, the oil is introduced through line 29 would constitute a source of heat for the cracking of the heavy charging stock. The pressure utilized in the heating coil 25 must necessarily be high enough to force the oil into soaker 3 when that path of. travel is chosen, but ordinarily it may be said that the pressure in the heating coil 25 may range from a few atmospheres to several hundred pounds per square inch, most desirably being in the neighborhood of 200 pounds per square inch. The pressure utilized in the evaporator 9 may be controlled relative to the pressure existing in the several cracking coils by proper manipulation of the control valves in an obvious manner. A vapor phase soaking drum (not shown) may be used in conjunction with heating coil 25 if desired.

During the operation a heavy reux condensate is collected on trap-out tray 3l and is conducted through draw-off pipe 32, having pump 33,

through valved by-pass line 34, or alternatively through heating coil 35 into soaker 36 and is therein subjected to additional cracking in a manner similar to that desired in conjunction with soaker 3. A light reflux condensate is removed from fractionating tower 31 and forced through pipe 38 by pump 39 into heating coil 40, wherein it is raised to a relatively high cracking temperature and subjected to conversion, the resulting cracked products being introduced into the soaker 36 by way of transfer line 4l having control valve 42. Reference numeral 43 indicates the trap-out tray from which the lighter reflux condensate is withdrawn, and 44 indicates the furnace structure housing the heating coils 35 and 40. The heating coil 35 may be placed in or out of. operation, as desired, by manipulation of valves 45, 46, and 41. Whether or not the heating coil 35 would be used would depend upon the character of the heavy condensate withdrawn from trap-out tray 3| for introduction into the soaker 36. If this condensate is of such character that it can be cracked to a certain extent or even heated, without deleterious deposition of carbon, it may be passed through the heating coil 35 and therein subjected to sufficient heat to raise its temperature without causing injurious deposits of carbon in the coil. But if this stock is of a dirty or coke-forming character the use of the coil 35 may best be avoided.

From the soaker 36 the cracked and digested products are conducted through conduit 48, having control valve 49, into the base of evaporator 50, and are therein separated into vapors and liquid residue. The vapors pass upwardly through the tower around baiiie trays or other contacting devices 5I, then pass through vapor line 52 into the base of the fractionator 31, wherein they are subjected to reflux condensation in the usual way. A heavier reflux condensate is collected at the base of the tower and is withdrawn therefrom through draw-01T line 53 for passage to a following cracking stage or for use in any desired manner. A lighter reflux condensate is collected on the trap-out tray 43, as already described. Fractionated vapors of the desired end point are removed from the top of fractionating tower 31 to vapor pipe 54 and condenser 55, the resulting condensate being collected in receiver 56, this being, for example, gasoline distillate. In a` like manner, fractionated vapors are removed from the top of fractionating column l2 through vapor pipe 51 and condenser 58, the resulting condensate being collected in receiver 59, this also being, for example, gasoline distillate.

The heavier reiiux condensate from the base of fractionator l2 is subjected to treatment in a manner similar to that of the .gas oil introduced to the system through pipe 23. That is, the reilux condensate withdrawn from the base of fractionator I2 is conducted through pipe I3 under pressure generated by pump 60, thence through heating coil 6| located in furnace 62, wherein it is raised to a relatively high cracking temperature of, for example, 900 to 1000 F. under a, pressure of from a few atmospheres to several hundred pounds per square inch, and subjected to conversion. A vapor phase soaking drum (not shown) may be used with heating coil 6l, if desired.

,pipe 32.

The resulting cracked products are conducted through transfer line M, having control valve 63, into the base of evaporator 50, or alternatively through conduit 65 having control valve t6, into the soaker 30 in mixture with the heavy oil from When so introduced into the soaker, this highly heated condensate will supply part of the heat necessary to carry out the cracking of the heavy oil introduced into the soaker. Reference numeral 6l! indicates a trap-out tray from which a `heavy condensate may be withdrawn via line 68 for passage to another cracking Zone or for any desired use. Residue collecting in the base of evaporator 50 may be withdrawn from the process by way of draw-off line 69.

Liquid residue collecting in the base of evaporator 9 is withdrawn through conduit 'l0 and may be diverted directly from the process, or alternatively part or all of this liquid residue may be conducted through by-pass line 'H into conduit 32 for further conversion in the soaker 36, the ow of the residue being controlled by valves I2 and 73. When liquid residue from the base of evaporator 9 is passed to the soaker 36 it will, in most instances, be found preferable not to utilize the heating coil 35, since this liquid residue has very marked coke-forming tendencies. In case the heavy condensate is clean enough for coil cracking or heating and the residue too dirty for that purpose, the condensate may be passed through the heating coil 35 and the residue directly to the soaking drum 3E, by suitable pipe connections. An alternative operation would be to introduce the heavy condensate and/or residue into the heating coil i0 near the outlet for cracking and digestion thereof.

In conducting an operation according to my process, the charging oils introduced through pipes 2 and 23 may be reduced crude and gas oil derived from a common source of crude oil, for example, the gas oil being a conventional clean gas oil cracking stock, and the reduced crude being such as is usually charged to a viscosity-breaking operation, or even a heavier reduced crude. In the soaker 3 the temperature may suitably be about 880 F. and the pressure about 200 pounds per square inch, although the temperature may suitably range 50 degrees more or less higher or lower than the value mentioned. The pressure likewise is not critical but may vary considerably, for example, in the range of several atmospheres to 1000 pounds per square inch. The gas oil passing through the heating coil 25 is desirably raised to a cracking temperature of about 925 to 950 F., although higher or lower temperatures in the range of 900 to 1000 F. approximately are suitable. The pressure in this heating coil is preferably such that so-called vapor phase cracking may be carried out, e. g. about 200 pounds per square inch, although higher pressures ranging from 500 to 1000 pounds per square inch may be used if desired. Where pressures in excess of 200 pounds per square inch are utilized on the oils undergoing cracking, the pressure in the evaporator may be with benefit somewhat lower, this pressure suitably being about 200 pounds per square inch, for example. In the heating coil l'i the lighter reflux condensate from fractionator I2 is preferably subj-ected to a more drastic cracking operation than that taking place in the heating coil 25, an example of desirable conditions in the coil Il being a temperature in the range of 1000 to 1100 F., e. g. about 1050 F., and a pressure of from 500 to 1000 pounds per square inch, e. g. about 600 pounds per square inch. Similar conditions may prevail in corresponding heating Zones 6i and 40, as well as soaker 36. The heavy. distillate removed from trap-out tray 3l should be considerably heavier than that normally subjected to coil cracking as a clean stock and may have, for example, a boiling range extending upward from about 650 F. while the reflux condensate removed from the base of fractionator I2 is a clean gas oil condensate of the type ordinarily considered proper cracking stock for a conventional vaporphase cracking operation, or may be slightly lower in boiling point, falling, for example, in the range of 550 to 700 F., or thereabouts. The lighter reflux condensate removed from trap-out tray iii of tower l2 is a still lower boiling fraction, falling, for example, in the range of 400 to 600 F., although this cut may be similar to that ordinarily subjected to a reforming operation, then including the heavier ends of gasoline which it is desired to reform. For convenience in the claims the several condensate cuts from the evaporator and the base of the fractionating column and intermediate point in the fractionating column may be referred to, respectively, as heavy condensate, intermediate condensate, and light condensate. Two cracking stages have been illustrated, but if desired, the reflux condensate removed through pipe 53 and the heavy condensate removed through pipe 68, as well as the residue removed through conduit BQ, may be subjected to additional cracking in further cracking stages similarly operated.

While I have described a particular embodiment of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof may be made by one skilled in the art within the spirit of the invention as set forth in the appended claims.

I claim:

1. The process of treating hydrocarbon oil which comprises introducing heavy oil charging stock not suitable for use as clean cracking stock into a soaking zone wherein it is maintained at a` cracking temperature, introducing the resulting soaked products intov a rst separating zone wherein vapors separate from liquid residue, fractionating resulting vapors to form a heavy, an intermediate, and a light reflux condensate, passing said light reux condensate through a heating zone in a stream of restricted cross-sectional area to raise it to a high cracking temperature and introducing the resulting highly heated prod-- ucts into said soaking Zone to maintain the desired cracking temperature therein, removing said intermediate condensate, passing it through a second heating Zone in a stream of restricted cross-sectional area to raise it to a high cracking temperature, introducing the resulting cracked products into a second separating zone, fractionating the resulting vapors to form an intermediate condensate and a light condensate, passing said light condensate last-mentioned through a third heating zone in a stream of .restricted crosssectional area, introducing the resulting products at cracking temperature into a second soaking zone, and introducing said heavy reiiux V condensate into said second soaking zone in such quantities that the resulting mixture in the soakingzone does not fall below an active cracking temperature and fractionating the products from the second soaking zone to-form a desired distillate.

2. The process of treating hydrocarbon oils which comprises introducing relatively heavy charging oil into a soaking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a first separating zone,fractionating the separated vapors to forman intermediate condensate and a light condensate, passing said light condensate through a heating zone in a stream of restricted cross-sectional area and therein raising it to a cracking temperature, introducing the resulting highly heated oil into said soaking zone in quantities sucient to maintain a desired cracking temperature therein, withdrawing said intermediate condensate and passing it through a second heating zone in a stream of restricted cross-sectional area and therein raising it to a cracking temperature and subjecting it to conversion, introducing the resulting cracked products into a second separating zone, fractionating the separated vapors to form an additional quantity of reflux condensate, passing reflux condensate so obtained through a third zone in a stream of restricted cross-sectional area and therein raising it to a cracking temperature, introducing the resulting highly heated products into a second soaking Zone in mixture with liquid residue withdrawn from the first separating zone, subjecting the mixture to conversion in said soaking zone, passing the resulting cracked products from the second soaking zone into the second separating zone, and condensing light fractionated vapors from the fractionating operation to form a desired light distillate.

3. The process of treating hydrocarbon oil which comprises passing a clean distillate cracking stock through a heating zone in a stream of restricted cross-sectional area wherein it is raised to a cracking temperature and subjected to conversion, introducing the r-esulting cracked products into a vapor separating zone, subjecting resulting vapors to fractionation to form a heavy reflux condensate, an intermediate condensate and a light reflux condensate, passing said light condensate through a separate heating zone in a stream of restricted cross-sectional area, wherein it is raised to a relatively high cracking temperature and subjected to conversion, mixing with the resulting highly heated cracked products heavy oil not suitable for use as clean cracking stock, in quantities insufiicient to reduce the temperature of the mixture below a cracking value, maintaining the mixture at a cracking temperature for a sufficient time to cause cracking of the added heavy oil and introducing the resulting cracked products into said vapor separating zone, passing the intermediate condensate removed from the ractionating zone through a third cracking zone in a stream of restricted cross-sectional area wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a second separating zone and subjecting the vapors so obtained to fractionation to form an intermediate condensate and a light condensate, diverting said intermediate condensate from the process, and passing said light condensate through a fourth cracking Zone in a stream of restricted cross-sectional area and therein subjecting it to conversion under relatively high temperature, introducing resulting cracked products into said second separating zone, mixing aforesaid heavy reflux condensate with said cracked products prior to their introduction into said second separating zone in such quantities that the resulting mixture does not drop below a cracking temperature, and maintaining the mixture at a cracking temperature for a sufficient time to cause cracking thereof prior to its introduction into said second separating Zone.

4. The process of treating hydrocarbon oil which comprises passing a clean distillate cracking stock through a heating zone in a stream of restricted cross-sectional are-a wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a vapor separating Zone, separating a heavy fraction from the oil introduced thereinto, subjecting resulting vapors to fractionation to form an intermediate and a light reflux condensate, passing said light condensate through a sepa-rate heating zone in a stream of restricted cross-sectional area, wherein it is raised to a relatively high cracking temperature and subjected to conversion, mixing with the resulting highly heated cracked products heavy oil not suitable for use as clean cracking stock, in quantities insuicient to reduc-e the temperature of the mixture below a cracking value, maintaining the mixture at a cracking temperature for a sufcient time to cause cracking of the added heavy oil and introducing the resulting cracked products into said vapor separating zone, conducting aforesaid heavy fraction to a separate cracking zone wherein it is raised to a cracking temperature and subjected to conversion by admixture therewith of the highly heated cracked condensate, introducing the resulting cracked products into a second separating zone, iractionating resulting vapors to form an intermediate condensate and a light condensate, diverting said intermediate condensate from the cracking operation, passing said light condensate through a third cracking Zone and raising it therein to a relatively high cracking temperature, introducing the resulting highly heated products into said separate cracking Zone to maintain the desired cracking temperature therein, and passing said intermediate condensate derived from the initial ractionating operation through a fourth heating zone in a stream of restricted cross-sectional area wherein it is raised to a cracking temperature and subjected to conversion and introducing the resulting cracked products into said second separating zone.

5, In the cracking of hydrocarbon oils, the process that comprises introducing charging stock into a heating zone and heating said stock therein to a cracking temperature to effect cracking, separating resultant cracked products into vapors and residue in a separating Zone, fractionating the separated vapors in a fractionating zone to form a heavy condensate and a lighter condensate, directing the lighter condensate to a separate heating zone and heating it in a flowing stream therein to a cracking temperature, heating a cycle condensate to a cracking temperature in a separate heating zone, combining said heavy condensate and said heated cycle condensatewith said lighter condensate, after the latter has been raised to a cracking temperature, to thereby raise the heavy condensate to a cracking temperature and subject it to cracking and advancing the resultant commingled products to a second separating Zone wherein separation of vapors from residue takes place, and fractionating the separated vapors in a second iractionating zone to form a light distillate and a condensate constituting said cycle condensate.

6. In the cracking of hydrocarbon oils, the process that comprises introducing a gas oil charging stock into a heating zone and heating said gas oil therein to a cracking temperature to effect cracking, separating resultant cracked products into vapors and residue in a separating zone, fractionating the separated vapors in a fractionating Zone to form a heavy condensate, an intermediate condensate and a lighter condensate, directing the intermediate condensate to a separate heating zone and heating it in a iioW- ing stream therein to a cracking temperature, combining said heavy condensate with said intermediate condensate, after the latter has been raised to a cracking temperature, to thereby raise the heavy condensate to a. cracking temperature and subject it to cracking and advancing the resultant commingled products to a second separating zone wherein separation of vapors from residue takes place and fractionating the separated vapors, directing said lighter condensate to a separate heating zone and heating it in a flowing stream therein to a cracking temperature, introducing a residuum charging stock into the stream of lighter condensate, after the latter has been raised to a cracking temperature, to thereby raise the residuurn stock to a cracking temperature and subject it to cracking and subije-cting the resultant commingled products to fractionation to form a desired distillate.

HAROLD V. A'I'WELL.

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