US2133096A - Process for cracking oils - Google Patents

Description

` W. KA HOLMES PROCESS FOR CRAOKING OILS Oct. 1v1, 193s.

Filed July v 25', 1928 Aga/mm..

latented ct. 11,1938` 'l i i OFF-1GB f will 1r. niimes, Part Arthur,4 rx.,'as`sigiidr to The Texas Compan New York, N. Y., a,v corporation of Delaware v Y Applitionrjuly 192s, sieriaiV d a jciaiiiis,V (c1. '19e-'49) `This invention has referenceto the production stage', thus'eliminating ,the necessity lfor further ofgasoline, or similar light hydrocarbons through distillation ofthe tar. v the cracking or conversion of higherboiling oilsA xAnother feature of the. invention in the into lower boiling oils by the application of heat provision-ofaplurality of vseparate heating units, and pressure;v Itrelates,particularlytothe ds-r such coils,y in a systemlof Athe. above general position Aof the heavy residual oils which `result character so A,that the several oil bodies requirfrom ordinaryprocesses-foreffecting conversion ing the' applicationrof heat may be subjected ofthe character mentioned. v l Y z to the-conditions most suited to their require-A Aniobject oftheinventionv is to provide for ments; Thus-'thelighter condensates Whichjare it) maximum eiiiciency in the utilization of theheat `knocked backgingthefractiQnatiOn' .0f the VaDQIS il0 employedin the cracking process. In attaining generated the system maybe subjected to' this. end, itis proposed to provide a closed cyclicY somewhat l different treatment from the fresh system which, in theeourseof` operation, will Vchargeof'oil being constantly introduced finto bring about the formation ofeonly two nal prodthe System. 'llrthlfditntm as. JO OPBIBf- 5, ucts in the nature of alight, marketable gasoline ing conditions mayV bebrought about 'between the' 115.

product and a heavyfuel oil. Incidentaltothe twdeondensates evolved, Vi. e., that'evolved from accomplishment ofl the foregoingjresult it is Y the fractionation of the vapors-from the pres-r contemplated to strip the residual material refr` suref cracking system and thatevolved from the sulting from the conversionvinl Ysuch a Wayasto fractionationjofithe vapors .released in the tar V yield -a maximum amount ofthe lighter,oils,as stripping chamber. i v 2g i5., er resiiiulal.v material is af99mp1ished ie ieesiasle* infreyieed Welleas stock Which may be recycled fornfrurther :A still further feature of they invention has cracking.. By virtue of-this phase ofthe process,r` todo with 1a; preferred and advantageous mode f there Vis brought abouta greatentotal yieldof of operationfof the system with particular refthe lighter constituents sinceithere is notonly erence to the amount of backtrap or condensate effected a more complete separationof thetdef returned-froznjthe fractionatorassociated with 25 siredlighter ends, butta greater percentageof the onversinunit to such unit Heretofore, the intermediate constituentszvvhich may beefit been the usual practiceto return condene fectively Vsubjected Lto ,further'cvcracking areyree sate, ofthis ;characterin/ an amount less than cycled while hot. Y l l twice themountfcf fr eshcharge introduced into Briefly, the invention has in view the employ-f' the system end frequently little more than equal 30 ment ofV a tar or residue distillation chamber to the a'monntof fresh charge. '.It has been directly in conjunction with .a cracking systemV discovered, however, that the return `of a relaof anysuitable form in such :a way that the itivelylargeamount ,of zthiscondensate, say,for heat Whichvwould otherwise Abe* wasted is` put' to example; three '.Or fouror :more -times'the amount full advantage. This includes not only the uti.- of freshychargetbrings,about very, advantageous 35 lization of the heat content of the residues them-` results,y particularly in. a system. embodying the selves, but also of the heat of VVthelue gases which several features of thepresent g invention. One are generated in the course of heating thestills obviousjl=idvari`tiitgeis that therspeed of lilovv of embodied in the cracking units; Toward` this the*liquid,vcombined`chargeiandxreturned con-` 40 end it is proposed to Vmount an expansion cham-k densate through the heatingcrunitysuch as acoil; 4o ber directly in the furnace surrounding the ',stills, is` increased toIsuch anv extent vthat thedanger or ,otherwise directly in the path of theiluegases oifdepositing carbon: and:delve1oping hotspotsis y from this furnace and to discharge .into such largely eliminated;` `vAttheV same 4time the burden chamber the residuestaken from the' stills. Due placeduponithe heating lunit .i'snot excessive due to a considerable reduction in pressure .on'the tjo itheatfthat the -Qcondensate returned Vto, it 45 oil, which is contemplated in its passagelinto alreadyjv ery hat; land needs to receive very the chamber, Volatilizationiv a largepercentage little jadditionalheet.: 1; y j j of thematerial will take placel immediatelyand fgwiththe 1; -foregoing Yandgotherv incidental .ob further volatile Constitutents will be' driven 0.1i; iectsandzadvantages in :view;...the invention win through the external application of theheat of now befdesc ibed detail by reference to thev .59 the flue gases or otherk source. By the applieaf` 'ac companyimgdmwngfinwhich thesinglegure tion of external heat Nto' the residue or tarfstrip` illystratesiiagganimatically Vone lsuitable form ping chamben. a satisfactory separationbetween of *p'paratusifory carrying v ont the invention. the ,.volatileconstituentsand `theheavier vfuel o il Referring vn w. helrawing,lthe1e maybe spugne; zgeoimectesi toseny- :suitable 5.5,

mizer by virtue of the fact that it is merely in the path of the ue gases'whioh are more directly applied to the heating of a lower `section|3 of the coil, or, if desired, thel two sections may constitute merely separate lportions of a single coil. From the outlet end of the economizer section i2, aline I5 is adapted to convey the Ycharge to the upper end of asecond heating coil I6 mounted in another furnace I1, whichmay re- Vceive heat from any suitable source.

A by-pass line I8 may be provided for the purpose of permitting all or a portion of the charge to flow` directly from the line II to the coilv I6, if desired-and for the purpose of regulating the yflow through the lines II, I5 and I8, a plurality of valvesY I9 ymay be suitably placed in the lines I I and I8. It is contemplated as desirable to maintain a pressure of between 150 and 600 pounds, preferably about 400 pounds, on the oil as it leaves the heating coils, although pressures outside of this range may be employed,

if desired. v

Upon leaving the coil I6, the temperature of the' oil` should be between 700 andv 950 FL, preferably about 850 F., and it may then be passed by a transfer line `ZIJ to one or more of a series of stills or drumsZi.

j 'While two `separate heating coils have been disclosed Vherein and form a partof 4ran ideal embodiment of the invention, this is not essential and one, for example coil I6, may be eliminated altogether, if desired.- If this is done, the charge, after fpassing through the section I2, will bepassed directly to the section I3 of the coil in thefurnace I4 and will emerge under the same conditions of temperature and pressure as explained above. To bring-about this elimination of coil I6, it will only be necessary to close a valve 22 in the'line I5 and open a valve 23 in a by-pass connection 24 communicating between the section lI2 and section i3 of the c'oil. In this event, the charge upon'leaving the lower end of the coil I3, may` be passed by a transfer line 25 to one or more of the series of stillsr2l.

It is not necessary thatmore than a single still or drum should be provided `but it hasbeen found preferable to employ a plurality of between two and four. Four have Vbeen illustrated in the accompanying drawing and" these are interconnected by means of a plurality of lines 26 which provide communication between the liquid bodies,r as well as thevapor'spaces of the several stills. vVlFl-'iile the stills may,V if desired, be. merely vheat-insulated, all' are preferably mounted within a furnace 21, which is heated byany suitable means and which is adapted to supply heat to the oil in the stills through the mid-portion of the walls ofthe latter. The heat so applied will preferably be only suii'icient to maintainA the temperature of the oil above the cracking point way of compensating Afor the heatk of v'apo'riz'`tionr Of'thelighter' constituents which pass'oi in vapor form".V f

ilAvapor linef, Yconnected tothe vapor space ofone or. more ofthe-stills, mayserve to con- 'aisaoce duct the evolved vapors to a dephlegmator o'r fractionating tower 29, which may suitably be of bubble tower construction. Here a separation between the heavier portions, which will be condensed, and the light portions, which will remain in vapor form, will take place. The lighter vaporous constituents may be carried through -a reflux condenser 30 housing the heat.

exchange coil I0 and through a line 3I to a suitable condenser 32, and into a storage or accumulator drum 33. Any suitable method may be adopted for providing a cooling medium, as by way of reflux, at the top of the tower 29; for example, a portion of the condensate collected inthe drum 33V may be carried through a pipe 34 to a pump 35, which may then serve to return it to the top of the tower through a line 36.

From time to time during the operation of the system, or continuously, if desired, the heavy residual oil which tends to collect in the bottom portions of the stills V2| may be drawn off through tar-drawing lines 31 and discharged into a main 38,Which.wi1l convey the residues to aneXpansion or pressure relief valve 39 and into an eX- pension chamber 40.1 Due to the heavy, tarry nature of the Vresidue so withdrawn, it will be found preferable to effect the withdrawal intermittently so that a greater flow may be provided at periodic intervals tokeep the connections 31 V free from obstructing carbon deposits. Where a battery of stills, such as illustrated, is employed, it will ordinarily be preferable to withdraw the tar more frequently from the last of the series and to withdraw it after only increasingly L greater intervals from the remaining stills. Suitable valves will be provided in the drawoait` lines 31 for controlling the withdrawal of the residue. In the event that continuous tar drawing is desired, it will be found advantageous to provide a by-pass line 31| aroundV the valve in the line 31 for, eay,-the last two stills. One or more of these by-pass lines may be kept continuously open to withdraw a portion of the residue as it accumulates. At the same time it will be found desirable to open up the lines 31 at periodic' intervals to draw ofi` greater quantities of the residue and keep these lines cleared.

Within the chamber 45 the pressure will preferably be maintained as near atmospheric as possible in order to produce a maximum flashing effeet, but it will be obvious that this pressure will fluctuate to a certain extent due to the intermittent introduction of at least a part of the residue into it. The chamber 40 may be provided with a series of baille plates 40| and suitable scrapers 402 and, as shown, is preferably mounted directly in the furnace 21, although it may be mounted in any other suitable way to receive the heat of the flue gases generated within the furnace 21 or to receive heat from other sources. It will be apparent that as a result of the reduction in pressure on the residue, and due to the additional heat applied to the chamber 40, a very large percentage of the oil will be ashed, or otherwise converted, into vapor, which may be carried through a vapor line CEI to any suitable form of dephlegmator or fractiona'tingcolumn v42. This may suitablyloe in the nature 'of a rock tower, or preferably a bubble tower. Those portions of the vapors which remain as such in their passage through the tower will becarried through a line 43 to a condenser 44 and may bedischarged into an accumulator drum 45.l A part Yof this condensate maybe returned by 'means of a pump 46 near that of the final product, it may be intro-v and a line 41 to the top of the column v42 as a means of cooling the latter. The products col-f lected in the drum 45 may, under certain conditions of operation, be in the nature of a marketfable grade of gasoline, as when the necessary cooling regulation is provided for the tower 42. However, it will be found preferable tooperate under conditions not calculated to produce a substantially finished gasoline at this "point, YFurthermore, it will be found that this product will at best have a greater tendency to go off color, due to polymerization of some of the constituents, thanis the case with the products collected in the drum 33. For this reason it may be found preferable to pass the remainder of the condensate collected in the drum 45 directly rinto the first mentioned fractionating tower Y29, where it will provide some of the necessary'cooling and reduce the requirement of refluxfrom'the drum 33. At the same time the condensate so subjected to further fractionation under pressurein rthe tower 29 `will undergo an action of polymerization which will tend to render the productcolor-stable. It will, in fact, pass in large part with the lighter vapors from the line 28 into the drum 33 as a good quality naphtha. c To dispose in this way of the part of the condensatenot returned to the column 42, a pipe connection 410 may be provided from thepump 46, or a separate pump may be employed if desired. It will be clear that it will be necessary to boost the pressure of the condensate by means of the pump 46 fromrsubs'tantially atmospheric to that maintained within the tower 29 and for this reason a different pump may be found preferable. If this modeof operation is adopted, the tower 42 may, if desired, be so regulated that a heavier productwillV be carried over, as for example a fraction including some of the kerosene constituents, although, preferably, the endpoint will be kept within the gasoline range. The point of entry o'f the condensate into the tower 29 will, for best results, depend upon the nature of the material. VIf its endpoint is duced through the line 410, while if its endpoint is higher, it may be introduced through the the condensate which is knocked back and which may be termed backtrap isY withdrawn by means of a pump 48 and maybe passed through a line 49 to the heating coil in the furnace I4. Various optional methodsY of handling the Ybacktrap through thelheating coil are afforded by the present disclosure.k The particular course through which it is desirable to force this condensate will depend largely upon the methodof handling the fresh charge of oil which is selected out of the several ways hereinbefore indicated. If the fresh charge is to be passed directly to the kcoil I6 through the by-pass line I8, previously described, then the backtrap may advantageously be passed through a line 59 to the upper end of the coil I2. At the same time the valves 22A and 23 should'be so adjusted that the re-heated backtrapwillbe passed through the coil I3 and be delivered into the transfer line 25 at a somewhat higher temperature than that of the fresh chargeof oil leaving the coil I6- This is done for the reason that the backtraped material is somewhat more dimcult to crack than the fresh charge and should pref- Y l3 being passed to the 'coil- I6, it will be advantageous to pass the backtrap directly to the inlet of the coil I3.' :To bring about this mode of operation, the line 50k-may be provided with a valve 5I which, When-closed,will tend toY direct the condensate into aline 52leading directly'to the inlet of the Vintroduce the backtrap at a lower point in the coil I3 where its temperature will correspond more nearly to that of the fresh charge. To enable the passage of the oil in this way, theline .52 may be provided with a valve 53 which, when closed, together with the valve 5I, will direct the 'condensate into a line 54 leading to a suitable pointnear the bottom of the coil I3. A valve 55 Yshould bevprovided in this Vline so as to close it ofi in the event that one of the first two mentioned modes' of-operation is adopted.

L Ina similar way'thecondensate which co1- Ylects at'the basel of the tower 42 and which may vbe termed cycle stock, is adapted to be withdrawn by means of a pump 56. Several optional courses may likewise be followed in the disposition of the cycle stock. It may, if desired, be passed through a line 51 to a point of juncture with the line 49 so as to merge the two condensates for passage in any one of the three ways indicated with respect to the backtrap. However, a different course may be found'desirable, particularly where the fresh charge is being passed first through the coil I2 andrthen the coil IE'. The cycle stock will be of a somewhat lower temperature than the backtrap whereas it will be of a considerably higher temperature than the fresh charge. "Its temperature may correspond more nearly to that of the charge after having passed through the coil I2 and for this reason it may be advantageously merged with the charge before the latter enters the coil I6, or, if desired, at an intermediate point in this coil. To effect this disposition vof the cycle stock, the line 51 maybe provided with a valve 58 which,when closed,*will direct the condensate into a line 59 joining the line I5 or entering the coil I6 at any suitable point. A valve 60 in the line 59 should be provided, so that when closed it will enable the passage of the oil in the iirst way indicated. Obviously, if desired, both of the valves 58 and IiIlA might beleft partially `opento any extent desired. to split the cycle stock between the two courses available to it.`

It has previously been suggested, as a feature of the invention, that the ratio of the backtrapped material to the fresh charge should preferably be quite large, for example in the neighborhood 'of three or fourto one. Thus, where a charging rate of, say, barrels per hour of freshv charge is maintained, the backtrap may to advantage y be returned to'the extent of 300 or 400 barrels per hour, or even more. It is to be understood, however, that thisis optional and that a smaller amount of backtrap may be developed, if de-4 sired. At the same time the cycle stock, or condensate from the` chamber 42, 'may well be 'developed in quantities of `100 to 300 barrels,'or more, per hour. although operations tending to produce somewhatless cycle stock than theY quantity of charge used are deemedpreferable. Where the backtrap and cycle stock assume the relatively high values mentioned, and the two heating coils are in operation, it will be found advantageous to pass the cycle stock through the line 59 directly to the coil I6, while the fresh charge is passed first through the coil I2 and then through the coil I6 and the backtrap is passed only through the coil I3. Operation of the unit in this way will bring about relatively high speeds of now of the material through the hotter portions of both the coils I3 and I6 so that the oil may be raised to a relatively high temperature without danger of excess deposition of carbon or theburning out of the tubes of the coils.

From the base of the expansion chamber 4I) a residue drawoff line 6I maybe provided and may serve to pass the heavy unvaporized portions of the tar to any suitable storage. This residue will be inthe nature of a heavy fuel oil fraction, which is unsuitable for further cracking but is of good quality for fuel purposes. It will be recognized that in the preferred mode of operating the system, only two products will be formed, these being the gasoline fraction collected at 33 and the fuel oil discharged through the line 6I. In addition, there will, of course,.be formed a small amount of coke and a small amount of fixed' gases but these maybe ignored.

While one suitable form of apparatus for carrying out the invention has been disclosed herein, and .certain definite operating conditions have beensuggested, it should be understood that these 'aregiven merely for the purpose of illustration and that many variations may be made within 'the scope and' spirit of the invention. It is desired to be limited in the application of the invention only by the scope of the claims which follow:

What I claim is:

1. In a process for the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises passing fresh charging stock through a tubular heater and raising the oil to a cracking temperature therein, passing the oil. thus heated into a cracking still wherein the oil is subjected to cracking and vaporization under superatmospheric pressure, subjecting evolvedvapors to fractionation to condense and thereby separate heavier fractions therefrom, withdrawing residue from the cracking still and reducing the pressure thereon to effect vaporization, subjecting evolvedy vapors to fractionation to form a condensate, passing a portion of said condensate through said tubular heater and directing the heavier fraction and another portion of the condensate through a separate tubular heater, and thereafter passing the condensates from said heater to said cracking still.

2. In a process for the conversion' of higher boiling hydrocarbon oils into lower boiling ones, thev process that comprises passing fresh charging stock through a tubular heater in a heating zone and then through another tubular heater in another heating zone whereby the oil is heated to a cracking temperature, passing heated oil into a cracking still wherein the oil is subjected to cracking and vaporization under superatmospheric pressure, subjectingV evolved vapors to fractionation tocondense and thereby separate heavier fractions therefrom, withdrawing residue from the cracking still and reducing the pressure thereon to effect vaporization, subjecting evolved vaporsY to fractionation to form a condensate, passing a portion of said condensate through the tubular heater in the second mentioned heating zone, directing said heavier fraction and another portion of said condensate through' a separate tubular heater in the first mentioned heating zone and thereafter passing the condensates to said cracking still.

3. In a process for the conversion of higher boiling hydrocarbon oils intoV lower boiling ones, the process that comprises passing fresh charging stock through a tubular heater in a heating zone Vand then through another tubular heater in another heating Zone whereby the oil is heated to a cracking temperature, passing the heated oil into a cracking still wherein the oil is subjected to cracking and vaporization under superatmospheric pressure, subjecting evolvedvapors to fractionation to condense and'thereby separate heavier fractions therefrom, conducting the heavier fraction through a separate tubular heater in said first mentioned heating Zone, withdrawing residue from the cracking still and reducing the pressure thereon to effect vaporization, subjecting evolved vapors to fractionation to form a condensate, passing a portion of said condensate through said second mentioned heating zone, directing another portion of said condensate into the Aseparate tubular heater in the rst mentioned heating zone and thereafter passing the condensate to said cracking still.

WILL K. HOLMES.

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