US2113816A - Process of treatment of hydrocarbon oil - Google Patents

Description

April 1938- c. w. SAACKE PROCESS OF TREATMENT OF HYDROCARBON OIL Filed Oct. 18, 1934 m m w m CHARLES n4 s/mcnz A TTORNEY Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE PROCESS OF TREATMENT OF HYDRO- CARBON OIL Application October 18, 1934, Serial No. 748,823

2 Claims.

This invention relates to processes and apparatus for the production of gasoline or other relatively light distillate from raw crude oil, or other similar relatively heavy stock containing lighter and heavier constituents.

In the treatment of raw crude oil or the like to produce gasoline, it has been the general prac tice heretofore to form from the crude oil, either by distillation alone or distillation coupled with mild cracking, a distillate stock suitable for charging to a cracking operation, this stock usually being a gas oil. Simultaneously, a plurality of other cuts have customarily been removed from the crude charging stock, being, for example, a light naphtha cut or virgin gasoline, heavy naphtha which it is desired to reform, kerosene and in some cases furnace oil, for sale as products without further conversion. After these several cuts have been obtained, it has 20 been customary to subject the gas oil to cracking in a separate unit, wherein it is converted to gasoline or other desired light distillates, and to reform the heavy naphtha separately in still another operation. In certain instances the re- 5 duced crude freed of the distillate stock mentioned, has been cracked under low crack per pass conditions to reduce its viscosity by the formation of additional quantities of gas oil suitable for cracking in a separate gas oil cracking 30 step.

It is an object of my invention to provide a unitary process for the treatment of raw crude oil or the like whereby all the operations necessary to produce a maximum amount of gasoline 35 of final desired end point and characteristics may be carried out at the same time in a series of interlocking steps so related, one to another, that a minimum amount of heat and attention are necessary, and high efficiency results. By

40 combining all of the various steps which have -heretofore been performed individually or in some incomplete combination, it is possible to utilize more advantageously heat which might otherwise be wasted, and also keep at a low figure the amount of'labor and supervision necessary in the operation of a system to carry out the process. I

More specifically, it is an object of my invention to combine in a single unitary process for the 50 treatment of raw crude oil, the steps of topping the raw crude, viscosity breaking the topped crude, cracking a clean condensate stock, including cracked and virgin components, derived from the process, reforming any necessary portion of 65 the gasoline produced to raise its anti-knock value to the desired point, and separately cracking a heavy gas oil distillate derived from the other cracking steps, under the condition best suited for the conversion of this heavy gas oil stock. 5

The above mentioned and further objects and advantages of my invention and the manner of obtaining them will be made clear in the following description taken in conjunction with the accompanying drawing. 10

The single figure of the drawing represents diagrammatically in side elevation and partly in section a combination cracking unit constructed in accordance with my invention.

Referring more particularly to the drawing, 15 reference numeral I indicates a crude flash tower,

2 an evaporator, 3 a viscosity breaking furnace, 4 a vapor phase furnace, 5 a soaking drum and B, a fractionator.

Fresh heavy charging stock, such as crude oil, after preliminary heating to a distilling temperature, for example, by indirect heat exchange with hot products resulting from subsequent cracking steps, or after having been heated in a directly fired coil, or both, is forced through charging line i by pump 8 into the first stripping section 9 of the crude flash tower or stripping tower I, wherein lighter constituents thereof are separated as vapors and passed off through vapor line it and condenser II into receiving drum I2, the condensate collected in the receiving drum being, for example, light naphtha or low end point virgin gasoline. The unvaporized liquid collecting in the base of the section 9 travels downwardly through pipe I3, into the intermediate portion of the second section I4 of the crude flash tower, wherein a further separation into vapors and liquids takes place, by the contacting of the introduced liquid with a stream of highly heated vapors passing upwardly through the 40 section M, as will be explained more fully hereinafter. This separation may be further aided, if desired, by a reduction in pressure obtained by adjustment of valve I5. The vapors generated travel upwardly through the section I4, and those remaining uncondensed at the top of this section pass oif through vapor line I6 and condenser I'I into receiver I8, the distillate so collected being, for example, heavy naphtha which it is desired to reform. An intermediate condensate collects on trap-out tray I9, and is forced by pump 20 through line 2i into the top of the evaporator 2 or into the bubble tower or fractionator 6 through line 22, or both. The intermediate distillate so introduced into the evaporator and/or fractionator serve as a refluxing medium, and is at the same time placed in a position for circulation through the vapor phase cracking furnace as will be explained more fully hereinafter. The unvaporized liquid collects on trapout tray 23, from which it may be withdrawn through pipe 24.

The several sections of the crude flash tower or stripper l are provided with bubble trays, baifles or other contacting means, as shown in the drawing, in accordance with the usual practice. The lower portion of the section i4 serves as a tar flashing chamber, as will be explained hereinafter.

Reference numerals 25, 26'and 21 indicate refluxing lines through which cool oil from an external source may be introduced for cooling and refluxing purposes in the well known manner. Alternatively, indirect cooling coils may be placed in the tower l, to accomplish the same purpose, or cooling may be supplied in any well known manner.

The unvaporized liquid reduced crude is withdrawn from the trap-out tray 23 through conduit E i, and forced by pump 28 through the heating coil located in the viscosity breaking furnace 3, from which the oil emerges, after having been raised to cracking temperature and cracked suiflciently to produce additional quantities of light clean gas oil stock, suitable for cracking in the vapor phase, and is forwarded through transfer line 29 into the lower portion of evaporator 2, wherein separation of vapors from liquid residue takes place. Valve 39 is inserted in the transfer line 29 to control the relative pressures in the viscosity breaking furnace and evaporator. The vapors pass upwardly through the evaporator, undergoing partial condensation therein, this condensation being only sufficient to condense the heavier gas oil components thereof, the vapors remaining uncondensed passing oif through conduit 3i and partial condenser 32, into the lower portion of the bubble tower 6. Condensate formed in the partial condenser 32 may be returned through conduit 33 to the top of the evaporator Zasa refluxing medium. The partial condenser may be omitted if desired. 7

'In the fractionator or bubble tower, 6, the vapors pass upwardly and are subjected to fractionation in the well known manner. Gasoline vapors remaining uncondensed at the top of the fractionator are withdrawn through pipe 34 and condenser 35, the condensate formed being collected in receiver 35. This condensate will be gasoline of the desired end point. It may be used by itself, or it may be combined with the light naphtha derived from the crude flashing operation and collected in the receiver !2. Either or both of these distillates may be stabilized, if desired, or be subjected to any other suitable treatment to give them the selected characteristics.

Reflux condensate collects in the base of the bubble tower 6, is removed through conduit 31, and passed by pump 38 through the cracking coil 39. of the vapor phase furnace wherein it is raised to a cracking temperature and subjected to conversion, preferably in the vapor phase. The resultingcracked products emerge from the heating coil and travel through transfer line 40 into the soaker or reaction chamber 5, wherein they undergo further conversion as a result of their contained heat, preferably under substantially the same pressure as held on the outlet of the heating coil. The digested products emerge from the soaker and travel through conduit El having pressure control valve 42, into the lower portion of the evaporator 2, wherein these products undergo separation into vapors and liquid residue, just as described in connection with the cracked oil from the viscosity breaking furnace 3, The soaker 5 may be by-passed, if desired, in which case the cracked oil from the heating coil 39 would pass directly into the evaporator 2.

The heavy naphtha collected in the receiver I8 is directed through the conduit 43, under pressure generated by pump 44, through the naphtha reforming coil located in the vapor phase furnace 4, wherein the naphtha is raised to a high cracking temperature suiflcient to cause the conversion thereof into higher anti-knock gasoline components. The resulting reformed products are transferred from the coil 45 through the line 45, having pressure control valve 41, into the lower portion of the evaporator 2.

A heavy gas oil condensate is collected on the trap-out tray 48 located in an intermediate level in the evaporator 2, is withdrawn through pipe 49, into accumulator 5t, from which it is withdrawn by pump 5i and forced through cracking coil 52 located in the vapor phase furnace 4. In

this coil the oil is raised to cracking temperature and subjected to conversion into lighter products, including lighter gas oil suitable for cracking at higher temperatures in the vapor phase cracking coil 39. The resulting cracked products pass through the transfer line 53,. having pressure control valve 54, into the lower portion of the evaporator 2, and therein undergo separation into vapors and liquids, similarly to the cracked products already discussed.

A refluxing line 55 is shown for supplying cooling fluid from an external source to the evaporator 2 and another line 55 is shown for providing cooling fluid to the top ofthe fractionator 6, in well known manner. Indirect cooling coils might be used for accomplishing the same purpose, in which event the cooling fluid might be the fresh charging stock, whereby the charging stock would be raised in temperature to aid in the distillation thereof. The evaporator 2 is provided with bafiie plates, bubble trays, or other suitable contacting means in a well known manner. I have indicated all of the cracked products from the several cracking and reforming coils 39, 45 and 53, as entering the evaporator 2 through a common connection. Instead all of the pipes 4|, 16 and 53 might connect separately with the evaporator. Cooling oil can be introduced into the soaker adjacent the outlet thereof and likewise into the various transfer lines, for fluxing purposes, in a well known manner, if desired, so as to inhibit the deposition of coke. Likewise any suitable cooling arrangement may be provided for maintaining the temperature of the liquid coilecting in the base of the evaporator 2 at a suitably low value to prevent deleterious coke deposition therein.

The liquid residue collecting in the base of evaporator 2 is withdrawn through conduit 51,

stock moving downwardly through the lower portion I4 of the tower, after introduction thereinto through the aid of conduit I3.

Reference numeral 60 indicates a valved line interconnecting the transfer line 29 with the base of the tower I whereby any desired portion of the hot products from the viscosity breaking furnace coil may be introduced directly into the crude stripping system along with the liquid residue from the evaporator 2, in order to supplyv any additional heat necessary for the final stripping of the crude charging stock.

All desirably light cracking stock contained in the residue introduced into the base of section 14, including any naphtha components, is volatilized, while the undesirably heavy constituents remain in unvaporized form and are withdrawn from the process through valved draw-off line 59. The heaviest fractions of the generated vapors are condensed and collected on trap-out tray 23 for By providing the several cracking coils shown,

it is possible to effect the desired conversion of the several oil components under the optimum conditions. The inclusion of the trap-out tray 48 and the associated heating coil 52 assures that the heavy gas oil, which is not suitable for cracking in the vapor phase furnace on account of coke forming tendencies, can be separately converted under the conditions best adapted to cause a maximum conversion thereof, without being returned to the viscosity breaking furnace 3, for conversion with the reduced crude at correspondingly lower conversions per pass. The provision of the cracking coil 52 also lightens the load on the viscosity breaking furnace 3 and .not only permits greater through-put or reduced crude in that furnace, but also limits the stock going through that furnace to a greater proportion of virgin components and to components which are more nearly of like characteristics. The viscosity breaking furnace 3 can, therefore, be operated under the best conditions for cracking the heavy reduced crude, while the heavy cracked condensate collected on trap-out tray 48 may be separately converted under conditions best suited to its characteristics, the clean gas oil cracking stock from the base of the fractionator and the heavy naphtha from the crude flash tower being separately treated in individual furnace coils, to cause the desired conversion thereof, under conditions properly selected for the stocks in question, without consideration for other of the fractions.

If desired the cracked products from the viscosity breaking furnace may be introduced into a separate evaporator, and only the Vapors be passed to the evaporator 2, part of these being diverted to the base of the tower l to supply additional heat, if desired. Or alternatively the vapors from the added evaporator may be separately fractionated in order to form gasoline distillate and light clean gas oil condensate suitable for vapor phase cracking, and heavier condensate, these condensates corresponding respectively to the condensates collected in the base of the fractionator 6 and the gasoline distillate so segregated can then be combined, either with or without previous reformation, with the cracked gasoline collected in receiver 36 and/or the virgin light naphtha collected in receiver I2, to form a desired blended product. The heavier condensate obtained can be introduced into the top of the evaporator 2 above the tray 48, and the lighter clean condensate can be introduced into the base of the fractionator 6, or, if desired, both stocks might be introduced into the evaporator above the tray 48, or part or all below the tray 48 if desired, for cooling purposes. In any event the effect would be to cause the heavy condensate to pass through the heating coil 52 and the lighter condensate to pass through the heating coil 39.

The same effect might be obtained by passing both the light and heavy condensates directly into the charging lines 49 and 31, respectively, of the two cracking coils mentioned. In case the vapors from the separate viscosity breaker evaporator are fractionated, the pressure in the evaporator last mentioned can be considerably lower than that in the evaporator 2, since the condensate stocks obtained can be pumped to their destinations at increased pressure. On the other hand if the pressure in the viscosity breaker evaporator is maintained sufiiciently high the vapors therefrom can be introduced directly into the evaporator 2 under their own pressure.

By utilizing two separate evaporators it is possible separately to extract from the process tar from the viscosity breaking operation, and from the cracking and reforming operations, these two tars having diflerent characteristics, several different types of marketable fuel oil can be formed by properly blending them, or the two tars may be sold separately if desired. The suggested additional evaporator, fractionator, and associated pipe lines have been omitted from the drawing.

Referring specifically to the furnaces 3 and 4, it will be noted that the stock to be subjected to viscosity breaking cracking is first passed through tubes in a convection section of the furnace, then through tubes located in the radiant portion of the furnace, and finally through soaking tubes located in the cooler convection section of the furnace. The relatively light clean gas oil removed from the base of the fractionator is preferably cracked by passage entirely through radiantly heated tubes located in one of the two radiant or combustion sections of the twin fire box type furnace 4. The heavy gas oil withdrawn from trap-out tray 48 is preferably passed through a similarly located coil 52 in the other radiant section of the furnace 4, while the naphtha from the receiver IB first is conducted through the convection section of the furnace, and then through roof tubes in the radiant section of the furnace, 4. Obviously other flow arrangements might be used, and other types of furnaces, likewise. The heating tubes could, if desired, be located each in a separate furnace, although the arrangement shown is preferred.

From a relative point of view, the cracking conditions on the stock charged to the viscosity breaking furnace 3, the cracking coil 52, the cracking coil 39, and the reforming coil 45, will be increasingly more drastic in the order mentioned. Merely by way of example, the outlet temperature of the heating furnace 3 may be 890 F., more or less, the outlettemperature of the coil 52, 940 F., more or less, the outlet temperature of the coil 39, 975 F., more or less, and the outlet temperature on the reforming coil 45 may be 1050 F., more or less.

I prefer to use the temperatures and pressures already mentioned, for the viscosity breaking, cracking and reforming operations, particularly for producing gasoline'of approximately ootane number from a charging stock such as 37 A. P. I. Mid-Continent crude, but somewhat higher or lower temperatures and pressures may be used, the exact conditions being determined in each case by the character of the charging stock and the specifications of the final desired products. The octane number and other characteristics of the final desired product may be regulated by varying the cracking temperature, the cracking per pass of the individual stocks, or the total amount of cracking of these stocks;

7 The outlet pressures on all of the heating coils may be substantially the same, this being sufiicient to maintain. a pressure in the evaporator of about 200 pounds per square inch, the pressure in a the soaker 5 being slightly higher, and that in the bubble tower or fractionator 6 being slightly lower. These pressures may, if desired, be different, the necessary differential being main-,

tained by adjustment of the pressure control valves in the transfer lines.

It is sometimes advantageous to increase the pressure on the reforming coil 45, for example by several hundred pounds, to a value in the neighborhood of from 500 to 700 pounds per square'inch more or less. The pressures on the outlets of the other coils may similarly vary from a few pounds to several hundred pounds per square inch, but in general the pressure conditions specifically mentioned are desirable.

Similarly the temperatures may vary quite widely, depending upon factors such as thecharacter of the stock and the character of the final desired product. As a rule it is not possible to state exact temperatures, but as a general proposition the outlet temperature of the viscosity breaking furnace coil may fall in the range of 840 to 900 F., the outlet temperature of the vapor phase coil 39 mayfall in the range of 850 to 1000 F. and the outlet of the reformer coil may fall in the range of 1000 to 1100 F. The outlet temperature of the heavy gas oil cracking coil 45 would desirably fall in between that of the viscosity breaking heating coil, and the vapor phase cracking coil, being, for example, in the range of 850 to 925 F. The amount of conversion to products in the gasoline boiling range per pass may be from 6% to 15%, in the viscosity breaking coil desirably about 10%; 10% to 20% in the heavy gas oil cracking coil 52, preferably about 15%; and 15% to 25% in the vapor phase cracking coil and soaking drum, preferably about 20%. These conversions per pass are merely intended for general guidance, and are not inserted in a limiting sense.

Various valves shown on the drawing, but not referred to definitely by reference numerals, are intended for. obvious control purposes. Auxiliary heat exchanges, cooling coils, pressure, flow and temperature controllers, and other auxiliary apparatus have been omitted from the drawing in the interest of clarity, but could be provided in accordance with the teachings of the prior art.

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

I claim:

1. The process of treating hydrocarbon oil which comprises separating from raw crude oil light and heavy virgin naphtha and topped crude, cracking said topped crude, reforming said heavy naphtha, contacting vapors from a portion of the cracked topped crude with said raw crude oil to aid in the said separating step, combining another portion of the cracked topped crude with the reformed products and separating from the combined products a gasoline distillate, a gas oil condensate suitable for use as vapor phase cracking stock andaheavier condensate, cracking said condensates last-mentioned in separate cracking zones and'combining the resulting products with said cracked and reformed products first-mentioned prior to the separation thereof into said gasoline distillate and said condensates.

2. The process of treating hydrocarbon oil which comprises introducing relatively heavy charging stock comprising crude oil components into a primary fractionating zone of a stripping zone in countercurrent contact with a rising stream of highly heated vapors, removing from the primary fractionating zone unvaporized portions of the said charging stock and condensed fractions of the rising vapors, passing oil so removed in a stream of restricted cross sectional area through a heating zone wherein it is raised to a cracking temperature by passing successively through convectively and radiantly heated zones and subjected to'conversion, introducing a portion of the resulting cracked products into an evaporating zone wherein vapors separate from liquid residue, fractionally condensing resulting vapors to form 'a desired gasoline distillate, a relatively light gas oil condensate and a relatively heavy gas oil condensate, passing said gas oil condensates through separate heating zones in streams of restricted cross sectional area and therein raising said oils to cracking temperature substantially only by the application of radiant heat and causing conversion thereof, introducing the resulting cracked products into said evaporating zone, removing liquid residue from said evaporating zone and introducing it into said stripping zone, with an accompanying reduction in pressure to cause the flashing of lighter constituents therefrom as vapors, the resulting vapors passing to said primary fractionating zone to constitute a source of said highly heated vapors firstmentioned and introducing another portion of the hot cracked products from said heating firstmentioned into said stripping zone to serve as an additional source of said highly heated vapors first mentioned.

CHARLES W. SAACKE.

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