US2016950A - Conversion of hydrocarbon oils - Google Patents

Description

Oct. 8, 1935. R. F. TROW CONVERSION OF HYDROCARBON OILS Filed May 4, 1933 x'ff. 314ML" ATTORNEY pors and residual oils in liquid form are sepa.- 25

Patented Oct. 8, 1935 UNITED ASTATES A PATENT oFFlcE CONVERSION F HYDBOCARBON OILS y Richard FfTrow, Port Arthur, Tex., assignor to The Texas Company, New York, N. Y.. a corporation of Delaware Application May 4, 1933, Serial No. 669,301

8Claims.

tillate of high antiknock value and a low yield of heavy distillate or fuel oil from a dirty stock,

that is to say, a stock which cannot be subjected to a drastic cracking operation producing a high yield of Vgasoline per pass without excessive coke formation. y

My invention has for further objects such additional improvementsin operative advantages and results as may hereinafter belfound to obtain.

My invention is especially applicable to an operation conducted for the purpose of converting hydrocarbon oils to oils of lower boiling point in which a stock is subjected to cracking conditions of temperature and pressure, as for example, while passing through a heating coil, the cracked products being delivered to one or more enlarged reaction vessels or stills from which varately withdrawn, and more especially to operations in which liquid is withdrawn from the reaction vessel or vessels at a rate sumcient to prevent liquid from accumulating within the reaction vessel or vessels and topreventdigestion of liquid within the same, while permitting digestion of vapors therein at a cracking temperature.y

' My invention contemplates heating a charging stock, such, Vfor example, as a dirty gas oil or a reduced crude resulting from a previous topping operation, to Aa moderate cracking temperature and soaking the heated stock, preferably in a separately fired soaking coil, to break or reduce the viscosity of the stock without causing deposition of coke to an undesirable extent, and discharging the viscosity broken stream into a distilling zone supplied with hot vapors produced elsewhere in the system. In the distillation zone, the more volatile constituents of the viscosity-broken stream are vaporized and the resultant vapors, together with other vapors from the distillation zone, are fractionated or dephlegmated, for exampie, by indirect contact with a stream of relatively cool charging stock or by reuxing with a suitable oil, to recover therefrom a clean gas-oil indicated, that is to say, at relatively high temperature and preferably in the vapor phase, the cracked products being delivered to one or more enlarged reaction vessels or stills from which unvaporized or residual liquid is preferably withdrawn at a rate sumcient to prevent accumulation of liquid in the reaction vessel or vessels. The residual liquid thus withdrawn may be treated for the recovery of the more volatile constituents thereof, while the vapors pass to the distilla- 10 tion zone where they are brought into contact with the viscosity-broken charging stock.

Unvaporized oil collecting within the distillation zone may be delivered to one or more of the reaction vessels or stills, either directly or by l5' being commingled with the stream of cracked products entering the same from the high-temperature or vapor-phase cracking coil.

My invention further contemplates cooling a portion of the clean gas oil or other interme- 2,0 diate fraction recovered by fractionation and dephlegmation of the vapors as set forth hereinabove, and the delivery of the resultant cool oil to the distillation zone for purposes of dephlegmation and to prevent coking.

With regard to the conditions under which the viscosity breaking of the charging stock is carried out, it may be said that, in general, the temperature employed will be suflicient to produce a material reduction of the viscosity of the charging stock without causing the deposition of coke to a material extent and to effect a hunted amount of cracking per pass, for example, from 6% to 8% of gasoline per lpass and at the most v not over 12% of gasoline per pass. The effect of 35 this treatment is, however, to make it possible ultimately to obtain larger yields of valuable light cracked distillate from a dirty charging stock without excessive coke formation.

In order that my invention may be clearly set 40 forth and understood, I now describe, with reference to the drawing accompanying and forming part of this specication, a preferred manner in which my invention may be practiced and embodied. In this drawing, 45

The single gure is a more or less diagrammatic elevationalview of apparatus for accomplishing the conversion of hydrocarbon oil to oils of lower boiling point in accordance with my invention. 5 In the drawing, there is illustrated a furnace I having a high-temperature hea-ting coil 2 and three enlarged reaction vessels or stills 6, 1`, and 8, although it will be readily understood by those skilled in the art tha-t the number of suchfves sels or stills may be varied in accordance with the requirements of individual instances. The distillation zone referred to hereinabove is located Within a suitable vessel I0 having baiiles I I, and the dephlegmation and fractionation of vapors removed from the vessel III is carried out in a suitable fractionating tower I2 which may be provided with a plurality of gas-and-liquidcontact trays or the like. shown diagrammatically at I3. Many specific forms of suitable trays are known in the art and n o particular type need be described here in detail. i

Further dephlegmation of vapors not condensed in the fractionating tower I2 may be accomplished in a dephlegmator I4 provided with a heat-exchange coil I5. As shown, the apparatus additionally comprises the condenser I6, a gas separator I1, cooling coils I8 and I9 and various conduits or transfer lines, valves and pumps which will be referred to hereinbelow.

In practicing my invention, a charging stock, such,' for example, as a dirty gas oil, a reduced crude or a mixture thereof, is withdrawn from a souice (not shown) through a conduit 2I by means of a pump 22 and may initially be passed in the manner indicated in the drawing through the heat-exchange coil I5, where, by indirect contact with vapors passing through the dephlegmator I4, the temperature of the charging stock may be brought to from 400 to 450 F. It will, however, be understood that if the charging stock is already in a heated condition there will be no advantage in passing the stock through the heatexchange coil I5 and this step may then be omitted. In the latter event, however, it is desirable to supply a suitable reflux oil to the fractionating tower I2.

'I'he heated charge oil then passes under elevated pressure through a conduit 23 to the economizer coil 3 within the furnace I, where the temperature of the charging stock is raised to a point sufiicient to support a moderate cracking or viscosity-breaking effect, for example, from 820 to 880 F., and preferably about 660 F.

The heated charging stock flows from the economizer coil 3 through a conduit 24 to the soaking coil 5 located within the furnace 4. Preferably, merely suilicient heat is provided in the furnace 5 to maintain the charging stock within the desired temperature range in order to complete the viscosity-breaking operation. However, if for any reason the oil should leave the economizer coil 3 at a temperature lower than the desired cracking temperature, sufliclent heat may be supplied to the tubes forming the rst portion of the coil 5 through which the stream passes to raise the oil to the desired temperature, and the oil is then soaked for a sufficient time at this temperature in the remaining portions ofv -the coil 5.

The viscosity-broken stream leaving the coil 5 then passes through a transfer line 25 to the distillation vessel I0, which it enters at an intermedia-te point.

Within the vessel I6, the viscosity-broken stream is subjected to direct contact with hot vapors from the still 8 entering the lower portion of the vessel I6 through a. conduit 25, and a combined volatilizing and dephlegmating effect occurs,.resultingvin the vaporization of the more volatile constituents of the viscosity-broken stream. The combined vapors reaching the top of the distillation vessel I0 pass through a vapor line 21 to the lower part of the fractionating tower I2, where dephlegmation is carried out to a sufilcient extent to produce a liquid fraction comprising a gas oil or the like which collects 5 lin 'the lower portion of the fractionating tower I2 and is withdrawn through a conduit 28. A portion of this gas-oil fraction may be withdrawn through a branch conduit 29 having a valve 3I and after being cooled in the cooling coil 10 I8 may be delivered by means o! a pump 32 and a reiiux line 33 to the upper part of the distillation vessel I0 in sumcient amount to provide a limited dephlegmation of the vapors within the latter and to prevent the formation of coke on 15 the bailles II.

The remaining portion'of the clean gas oil fraction or recycle stock removed from Ithe bottom of the fractionating tower I2 is withdrawn through abranch conduit 34 having a valve 35 and 20 is delivered by means of a pump 35 and a conduit 31 to the vapor-phase cracking coil 2 locatedv in the furnace I, where it is heated to a temperature sufficient to effect vapor-phase cracking, preferable at a high rate of cracking per pass, for example 25% or more. ThusI may employ ternperatures of from 900-to l000 F. and preferably about 915 F. The cracked products then pass through a transfer line 39 which may be provided as shown with a pressure-reducing valve 4I -to the upper part of the still 6. Within the still 6 a separation of vapors and liquid occurs. the vapors, and it may be a small amount of liquid oil, passing through a conduit 42 into the adjacent still 1. A further separation occurs in the latter and the vapors pass to lthe third still 8 through an overhead conduit 43.

As recited hereinabove, unvaporized liquids which tend to collect in the stills, 6, 1, and 8 are withdrawn from the latter by means of drain conduits 46, 41, and 48, having float-operated valves 5I, 52, and 53, respectively, at rates sumcient to prevent accumulation of liquid within the vessels or stills 6, 1, and 8. Preferably, merely enough liquid is permitted to collect within the 45 vessels 5, 1, and 8 to form a seal to prevent escape of vapors from the bottoms thereof. The residual oil or tar thus withdrawn is preferably delivered through a conduit 53a to a tar stripper 59 to be described more fully hereinbelow. 50

The unvaporized portion of the viscosity-broken stream delivered to the distillation vessel I0, together with any condensate obtained from the vapors entering the distillation vessel I0 through a conduit 26, is withdrawn from the lower part 55 of the distillation vessel I0 through a conduit 55 and delivered by means of a pump 56 through a conduit 51 having a valve 58 to the transfer line 39, or it may be delivered directly to the stills 6,

8, and 1. The residual oil thus withdrawn from 60 the bottom of the distillation vessel I0 may have a high temperature, for example around 850 F., and in treating certain stocks, a portion of the stream leaving the pump 55 may be by-passed through a line 6I having a valve 63 to the cooler 65 I9 and thence to the inlet side of the pump 55. In this instance, sufficient cooling is eiected in the cooler I 9 to reduce the temperature of the oil reaching the pump 56 to, for example, around 800 F. or even lower. 70

In the preferred method of operation, the introduction of combined condensate and residual portions of the charging stock, whether cooled or not, to the transfer line 39, is so regulated as to maintain a temperature of from about 870 to 75 about 830 Il'. in the stills 8, 1, and 8, maintenance of this temperature range facilitating the withdrawal of liquid from the stills '6, 1, and 8 and the maintenance of low liquid level" conditions therein.

' The uncondensed vapors leaving the dephlegmator I4 pass through a vapor line 65 to the conv denser I6 where they are cooled in the usual man- -ner, the cooled products then passing through a line L66 to the separator I1.` Gas and any uncondensed vapors are removed from the separator I1 through a conduit 61 having a valve 68, while light cracked distillate is removed from the separator I1 through a line 08. A portion of this condensate may be returned through a branch conduit 1I having a valve 12 and a pump 18 to the upper part of the fractionating tower I2k as a re-y flux. while the remaining portion or it may be all of the condensate from the separator I1 passes through a conduit 14 having a valve 1l to storage or to suitable apparatus for effecting stabilization thereof.

'Ihe -pressures maintained within the system may vary considerably but in general the pressures in the coils 2, 8 and 5 are maintained within a suitable range, for example, from 200 to 600 pounds per square inch. While similar pressures may be maintained throughout the system, it isy ordinarily preferred to maintain somewhat lower pressures, for example, from 150 to 350 pounds vpersquare inch, in the stills6, 1, and 8, the distillation vessel I0 and the fractionating tower- I2. In a modified form of my invention the pressure in the dephlegmator I0 and fractionating tower I2 may be reduced to 150 pounds per square inch, or evenlower, by means of 'a pressure-reducing valve 80' located in thevconduit 26.-

` As has been stated hereinabove the liquid withdrawn from the stills 6, "I, and 8 is preferably passed through a conduit 68a to a tar stripper 64. The tar stripper 84 may be varied in design but in the preferred instance illustrated it'comprises a flash chamber 6I having bailles 82 and a fractionating section 88 having suitable plates or trays 84. The chamber 8| and the fractionating section 84 are separated by a trap-out tray 8l and the upper portion of the fractionating section 84 is provided with a reflux inlet line 86.

The liquid withdrawn from the stillsv6, 1, and 8 in this instance passes through the conduit 53a wherein is located a pressure-reducing valve 81 by means of which the oil is reduced in pressure as it passes into the flash chamber 8 I The lower boiling constituents ofthe oil are thereby liberated in vapor form and passed upward into the fractionating section 83 through a vapor line 88 while heavy residual portions of the oil are withdrawn from the bottom of the iiash chamber 8| through a conduit 80 having a valve 8| and pref- A erably leading through a cooler 82 to fuel oil storage facilities (not shown). u

By means of reflux introduced through the line v86 or by cooling eiected in any other suitable manner the vapors passing through the fractionating section 83 or the tar stripper 54 are subjected to fractional condensation to such an extent as to effect the separation in liquid form of a'heavy gas oil fraction which is withdrawn from the trap-out tray 85 through a conduit 88 having the line 23 to the inlet of the coil 8, being thus therein.

The vapors remaining uncondensed at the top of the fractionating section 88 of the tar stripper s 64 pass through a conduit 81 to a condenser 88 where they are cooled to eifect a condensationof normally liquid constituents, the operationpreferably being conducted to recover at this point a distillate comprising either heavy 'naphtha constituents or light gas oil constituents or a mixture of these. The mixture of uncondensed gases and condensate then passes through a conduit 88 to a gas separator I8| having a valved outlet |82 through which uncondensed gases escape. The condensate' passes out of the separator |8| through a conduit |08 having a pump |04, by means of which it may be partly returned through the conduit 86' wherein is located a valve |08 to the tar stripper 84 as reflux. The remaining portion of the condensate recovered in the separator |0|, or it may be all of vthis condensate, is preferably delivered by the pump |04 through the conduit |88 anda conduit |86 having a branch |01 wherein is located a valve |88. 25 to the conduit 81 where it is commingled with gas oil recycle stock withdrawn from the bottom of the fractionating tower I2 and being delivered to the cracking coil 2.

In an alternative method of procedure, a portion or all of the condensate withdrawn from the separator I0| may be returned through conduits |08 and |06 and a branch conduit |09 having a valve ||0 to the fractionating tower I2 for use as reiiux therein. 35

It will be obvious to those skilled in the art that my invention is not limited to the specic details of the illustrative example or examples set forth and described hereinabove but may variously be practiced within the scope of the claims hereinafter made.

What I claim is:

1. The process of converting hydrocarbon oil into oils of relatively low boiling points which comprises heating a charge oil to a mild cracking temperature and soaking the heated oil substantially without reduction of temperature in a primary cracking zone to reduce the viscosity of the oil, passing the viscosity-broken products directly to a distillation zone into direct contact with hot vapors produced in the system, thereby vaporizing lighter fractions vof said viscositybroken products, passing vapors from said distillation zone to a fractionating zone and dephlegmating said vapors to recover therefrom a 55 light distillate and a heavier recycle stock fraction, subjecting said recycle stock to relatively drastic cracking conditions in a separate cracking zone, discharging the cracked products into therst of a plurality of enlarged reaction vessels 30 'arranged in series in each of which separation of i vapors from liquid products of reaction occurs, conducting separated vapors from one reaction chamber to the others in succession and from the last reaction chamber to said distillation zone, separately withdrawing separated liquid from each of said reaction chambers, withdrawing residual oil from said distillation stage and directing it to said series of enlarged reaction vessels.

2. The process vof converting hydrocarbon oil into oils of relatively low boiling points which comprises-heating a charge oil to a cracking temperature of the order of 820 F.-880 F. and soaking the heated oil substantially without reduction of temperature in a primary cracking zone broken products, dephlegmating the evolvedv vapors from said distillation zone to recover therefrom a light distillate and a heavier condensate, subjecting said heavier condensate to heating to eiect a high rate of cracking per pass in a. separate cracking lzone and directing the cracked products into an enlarged reaction zone,v

conducting residuefrom said distillation zone into said reaction zone, maintaining a temperature therein of the order of 870-930P F., witldrawling liquid constituents from said reaction zone at a rate adequate to prevent accumulation of liquid therein passing vapors from said reaction zone to a second reaction zone wherein the vapors are maintained at cracking temperature to eiect further cracking and directing vapors from said second reaction zone.

3. The process of converting hydrocarbon oil into oils of relatively low boiling points which comprises passing cycle condensate formed in the process through a high temperature heating coil wherein the condensate is heated at temperatures of the order of 900 F.-1050 F. to subject the oil to a high rate of cracking per pass, discharging the products from said heating coil -into an enlarged reaction zone maintained under cracking conditions and wherein separation of vaporfrom liquid occurs, withdrawing liquid constituents from. said reaction zone at a rate adequate to prevent the accumulation of liquid therein, passing only the separated vapors into a second reaction zone wherein the vapors are maintained at cracking temperature to effect further cracking, directing vapors from said second reaction zone to a distilling zone, heating charging stock in a primary cracking zone to a cracking temperature of the order of 820 F.-880 F. under conditions to effect a cracking per pass into gasoline constituents of about 6%-8% and effect a reduction in the viscosity of the charging stock, delivering the viscosity-broken products directly to said distilling zone into contact with aforesaid separated vapors introduced thereinto to eiiect distillation of the viscosity-broken products and condensation of a portion of said separated vapors, withdrawing from said distilling zone a liquid residue comprising residual constituents of said viscosity-broken products and directing said liquid residue to said enlarged reaction zone wherein it is in contact with the heated products discharged thereinto from the said high temperature heating coil and subjecting vapors evolved from said distilling zone toA fractionation to separate out a light distillate and a heavier condensate constituting the cycle condensate passed to the cycle condensate heating coil.

4. 'I'he process of converting hydrocarbon oil into oils of relatively low boiling points; which comprises passing cycle condensate formed in the process through a high temperature heating coil to subject the condensate to a high rate of cracking per pass, dischargingthe products from said heating coil into an enlarged reaction zone maintained under cracking temperatures of the order of 870 F.930 F. and wherein separation of vapor from liquid occurs, passing only the separated vapors into a second reaction zone wherein the vapors are maintained at cracking temperature to effect further cracking, directingv vapors from said second reaction zone to a distilling zone, heating charging stock in a primary cracking zone to a cracking temperature of the 5 order of 820 F.880 F. under conditions to efiect a cracking per pass into-gasoline constituents of about 6%'8% and effect reduction in the viscosity vot the charging stock, delivering the -viscosity-broken products directly to said distill- 10 ing zone into contact withaforesaid separated vapors introduced thereinto to eiect distillation of the viscosity-broken products and condensation of a' portion of said separated vapors, withdrawing from said distilling zone a liquid residue comprising residual constituents of said viscositybroken products and directing said liquid residue to said enlarged reaction zone wherein it is in contact with the heated products discharged thereinto from the said high temperature heat- .ing coil, withdrawing liquid from said enlarged reaction zone at a rate adequate to prevent the pors evolved from said distilling zone to fractionation to separate out a light distillate and a heavier condensate constituting the cycle condensate passed to the cycle condensate heating coil.

5. Apparatus for cracking hydrocarbon oils that comprises a cracking still, a distilling chamber adapted to receive vapors from the cracking still, a ifra'ctionating tower adapted to receive vapors from the distilling chamber and separate out condensate therefrom, a furnace formed to prgwide a main heating section and an economizer section, a high temperature cracking coil located in the main heating section of the furnace, means for conducting condensate from the fractionating tower to the high temperature cracking coil, a transfer line for conducting the products from the high temperature cracking 40 coil to the cracking still, a low temperature cracking coil located in the economizer section of said furnace, means for introducing charging stock to said low temperature cracking coil, a soaking coil adapted to receive the products from said low temperature cracking coil, means independent of said furnace for maintaining the soaking coil at a cracking temperature, means for conducting products from the soaking coil to said distilling chamber and means for conducting liquid from the distilling chamber to said cracking still.

6. Apparatus for cracking hydrocarbon oils that comprises a cracking still, fractionating means for separating out a condensate from vapors evolved from the cracking still, a furnace formed to provide a main heating section and an economizer section, a high temperature cracking coil located in 'the main heating section of the furnace, means for conducting condensate from the fractionating means to the high temperature cracking coil, a transfer line for conducting the products from the high temperature cracking coil to the cracking still, a low temperature cracking coil located in the economizer section of said furnace, means for' intro- 65 ducing charging stock to said low temperature cracking coil, a soaking coil adapted to receive the products from said low temperature crackaction zone where separation of vapor from liquid residue occurs and wherein the liquid residue is subjected to flash distillationin a flashing zone, the vprocess that comprises heating charging stock in a primary cracking or viscosity-breaking coil to a cracking temperature to eiect a reduction in the viscosity thereof, delivering the viscositybroken products into a distilling zone, passing vapors from. said enlarged reaction zone into said distilling zone into contact with said viscositybroken products thereinA to effect distillation of 'the viscosity-broken products and condensation of a portion of said vapors, subjecting the remaining vapors to fractionation to separate out alight distillate and a cycle condensate, passing said cycle condensate to a high temperature cracking coil wherein the oil is subjected to a relatively high cracking temperature to effect a high rate of cracking per pass and directed thence into aforesaid enlarged reaction zone, subjecting the vapors evolved in the' flashing zone to fractionation to separate out a lighter fraction and heavier fraction thereof, directing the heavier fraction to said viscosity-breaking coil and passing the lighter fraction to said high temperature cracking coil.

8. In the conversion oi.' hydrocarbon oil into oils of lower boiling points wherein hydrocarbon oil is subjected to cracking in an enlarged reaction zone where separation of vapor from liquid residue occurs and wherein the liquid residue is subjected to flash distillation in a flashing zone, the process that comprises heating charging stock in a primary cracking or viscosity-breaking coil to a cracking temperature to effect a reduction in the viscosity thereof, delivering the viscositybroken products into a distilling zone, passing vapors from said enlarged reaction zone into said distilling zone into contact with said viscositybroken products therein to effect distillation of the viscosity-broken products and condensation of a portion of said vapors, subjecting the remaining vapors to fractionation to separate out a light distillate and a cycle condensate, passing said cycle condensate to a high temperature cracking coil wherein the Oil is subjected to a relatively high cracking temperature to effect a high rate of cracking per pass and directed thence into aforesaid enlarged reaction zone, withdrawing from said distilling zone a liquid residue comprising residual constituents of said viscositybroken products and directing said liquid residue to said enlarged reaction zone wherein it is in contact with the heated products discharged thereinto from said high temperature cracking coll, subjecting the vapors evolved in the flashing zone to fractionation to separate out a lighter fraction and heavier fraction thereof, directing the heavier fraction to said viscosity-breaking coil and passing the lighter fraction to said high temperature cracking coil.

RICHARD F. TROW.

CERTIFICATE 0F CORRECTION.

iatent No. 2,016, 950.

October 8, 1935.

RICHARD F. TRow.

lt is hereby certified that error' appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, first column, line 24, claim 2, after "zone" insert the words to said distilling zone; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

. Signed and sealed this 19th day of November, A. D. 1935.

l I Leslie Frazer (Seal) Acting Commissioner of Patents.

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