US1936298A - Treating hydrocarbon oils - Google Patents

Description

Nov. 21, 1933. H. A. FOUTS TREATING HYDROCARBON OILS Filed Nov. 22, 1929 Patented Nov. 21, 1933 UNITED srATEs restais TREATING HYDROCARBON OILS Horace A. Fouts, San Antonio, Tex., assignor to The Texas Company, New York, N. Y., a ccrporation of Delaware Application November 22, 1929 Serial No. 408,967

4 Claims.

This invention relates to the conversion of higher boiling hydrocarbons into lower boiling ones, particularly for the production of lower boiling products such as gasoline and the like.

The invention contemplates a process in which a condensate formed in the process is subjected to a cracking temperature and fresh charging stock is brought into heat exchange with the oil undergoing cracking to prevent the cracking oil from reaching too high a temperature, such that the cracking reaction Would be carried too far, and at the same time raise the fresh charge to a distilling or a cracking temperature. In carrying on cracking operations at high temperatures, such for example as when cracking in the vapor phase, considerable diiiiculty has been experienced in preventing the highly heated oil undergoing cracking or portions of it from being overheated with a consequent excessive production of fixed gases and coke or carbon. The practice of my invention affords and method of overcoming this dificulty, since in practicing the invention the temperature of the highly heated oil undergoing cracking may be accurately controlled by heat exchange With less highly heated oil so that excessive cracking does not take place.

In a preferred embodiment of the invention condensate derived from the process is heated in a coil or tubular heater to the desired cracking temperature and the fresh charge is brought into heat exchange with the cracking oil either by introducing the charge into the coil or by passing it through a conduit in heat exchange therewith and the products, after' the heat exchange, are conducted to a Vaporizing chamber in which evolution of vapor occurs and the resultant vapor is subjected to condensation or dephlegmation to form the condensate oil that is subjected to the cracking operation.

The coil or tubular heater employed is preferably arranged so that the condensate oil charge may be subjected to progressively increasing temperatures and the heat exchange with the fresh charge is effected in the hotter portion of the furnace or at a point in the coil after the condensate oil has been brought to aproximately the maximum cracking temperature desired. Thus the condensate oil to be subjected to a high cracking temperature, such as a vapor phase cracking temperature, may be rapidly raised to the high temperature desired by passage through the coil in which the flowing oil is subjected to the action of combustion gases of progressively increasing temperature and When approximately the maximum temperature desired has been reached the relatively cool fresh charging stock may be brought into heat exchange with the highly heated condensate oil so. that any -material further rise in temperature may be prevented. Thus when the fresh charge is passed through a conduit in heat exchange With that portion of the condensate oil coil Which is positioned in the hottest portion of the furnace, the rapid increase initemperature which had been taking place in the first part of the coil is arrested, although the condensate oil may still be held Vat a temperature adapted for cracking. It is preferred that the system of heat exchange between the condensate oil and the fresh charge will be so arranged that, while any further material increase in temperature of the condensate oil is prevented, nevertheless it Will be held at a temperature at which cracking takes place and at the same time that the fresh charging stock will either be heated to a distilling temperature to effect the distillation of the more volatile products contained therein or that it may be brought even to a cracking temperature. f

In practicing the invention it is preferred to discharge the heated fresh charging stock and condensate oil into a vaporizingchamber for vaporization. Thus the commingled fresh charge and condensate oil which have been admixed `in the heating coil, or the separate streams of condensate oil and fresh charging stock, in casefthe indirect method of, heat exchange is employed, are directed into the vaporizingchamber. The evolved vapors are dephlegmated to formv the light distillate desiredand also the cycle condensate that is conducted to the heating coil for cracking.

One method of operation contemplated by the invention consists in drawing oifliquid oil from a vaporizing chamber and rapidly circulating it, as by bringing it into contact or heat exchange with heated products from a heating coil and returning the oil thus heated to the vaporizing chamber to thus promote the stripping or vaporizing of the Vliquid in the chamber. Thus a relatively heavy tar or residue may be Withdrawn from a lower portion of the vaporizing chamber and a stream of somewhat lighter material drawn from an upper portion of the body of liquid in the chamber and this stream brought into heat exchange With the heated products in the coil and returned to the vaporizing chamber. In this Way the heavier products are discharged from the system While the distillation or stripping of the body of oil in the chamber is facilitated by the rapid circulation and heat change.

Various other novel features as well as advantages of the invention will appear in the following detailed description thereof and in order to give a more complete description of the invention reference will now be had to the accompanying drawing wherein:

Figure 1 is a diagrammatic elevation partially in section illustrating a preferred embodiment of the invention.

Figure 2 is a partial sectional view illustrating a modified form of heating coil.

The apparatus illustrated in Figure 1 includes a heating coil 10, a still or vaporizing chamber 11 and a dephlegmator 12. The fresh oil charge to be treated is drawn from a suitable source by means of a pump 13 and forced through a charging line 14 and valved branch lines '15 Vto the heating coil 10. The vapors from the still are directed by ak vapor line 16l to the' dephlegrnator 12 which ispreferably in the forni of' a bubble tower or other suitable fractionating tower. The vapors from theVv tower pass through a vapor line 1'7 to a reflux condenser 18 provided with a return condensate line 19Yfor conducting resultant condensate to the tower 12 to serve as a cooling reflux therefor. The cooling arrangement for the reflux condenser 18 whichis indicated in the drawing includes a coil 20 provided with valvedV branch lines 21 and 22 extending to the charging line 141so that a portion or all of the fresh charge may be employed as the cooling medium.

Reflux condensate formed in the tower 12 is withdrawn by a line 23 extending to a hot oil pump 24 which forces the condensate through a line 25 tothebeginning of the heating coil 10. The latter coil is shown disposed in a furnace 26 provided with heating means 27; Thus it will be seenthat the oil in transit through the coil 10 may be subjected to combustion gases of progressively increasing temperatures so that the condensate oil may be rapidly raised to the cracking temperature desired. In the latter portion of the coil, however, which is subjected to the more intense heat of the furnace, this oil stream passing through the coil 10 is cormningled with the-relatively cool fresh charging stock which is being introduced through then line 14 and the branch lines 15. Iii-introducing fresh charging stock into the coil it maybe admittedV at one point as through one of the branch lines 15 or at a plurality of points through as many branch lines-15 as may be desired.

When the condensate oil which has been brought to the desired cracking temperature in the upper portions of thefurnace-Z 'comesincontactfwith-the relativelyy cool chargingstock any further increasegin Vtemperature of thecondensate oil may be ,prevented sov that excessive cracking thereofJ with resultant excessive production of fixed gases is avoided. Although the cooling cffected by. the introduction-offresh charge into the. coil 10 may be sufcient to reduce the tern" perature of the combinedfreshcharge and condensate oilto below a cracking temperature, it is preferredrthat the reduction in temperature shall not be as great as this, and thus the tempera-- ture ofthe combined oils be such that crac-ring will continue throughout the latter portion of4 the coil', although the temperature may be no'higher than that to which the condensatcoil had-been raised prior to theintroduction of` the fresh charge.

A. transfer line 28 serves to conduct the combined heated oils from the cracking coil l0 to the vaporizing chamber 11, a baille 29 being preferably employed to receive the oil thus discharged into the vaporizing chamber and over which baille the liquid flows. Although the practice of the invention does not preclude the application of heat to the still l1 it is ordinarily unnecessary to do so, since the still may be heat insulated and the hot products discharged through the line 28 will be found to supply suicient heat for the desired vaporization.

A tar leg 30 having an outlet line 31 is indicated for drawing oir heavy tar or residue from thefstill andit is prei-erred that the bottom of the still slope toward the tar leg to facilitate the removal of the heavier products through the tar leg.` A line 32 is shown for drawing off liquid from an upper level in the body of oil in the still, this line being preferably connected to the still at a point adjacent the liquid level thereofV and extending to a pump 33V whichoperates to draw olf liquid from near the upper portion of the body of oil in the still and pass the oilthus withdrawn through a 34 connected to the line 28 to thus bring the withdrawn'liquid into contact with the hot products passing through the transfer line 28; It is preferred that the circulation' of liquid thus withdrawn from the still be carried` on at a--rate comparatively rapidas compared to the rate of withdrawal of liquid through the tar leg 30 and line 31. Thus, for example, residue may be withdrawn through the line 31 at a rate of say- 20-to 3l) barrels per hour while the rate of circulation through the lines32 and 34niay be at the rate of say 106 barrels per hour. In this way the' contentsof the still which tend to cool hy'reason of the vaporization taking place therein are rapidly brought into contact with the hot stream-of oil passing through the line 28-'so that the maintenance of the desiredv distilling temperature in the still is facilitated.

The vapors from the refluxcondenser 18 are conducted through a line 35' to a condenser'coil Beand a receiving drum 37 having a gas outlet line 38 and a condensate outlet line 39. The distillate collected in the receiver 37 constitutes the gasoline or naphtha desired.l

In the modified arrangement shown in Figure 2 a heatingicoil loa is shown mountedin the fur# nace 25 supplied with heating means 27 andin the lower portion of the coil, that is that section thereof which is subjected to the hotter furnace gases, a coil 40 is mounte interiorly thereof. The refluxcondensate from the tower 121s admitted through the line 25 to the coil 10al and passes downwardly through the coil toA be'flnally delivered to the transfer line 41 for delivery into the still 11, a baille 42 being1indicated vfor directingl the flow of liquid thus dischargedinto the still. By having the coil 40 disposed interiorly of the coil 10a the cross sectional area ofthe coil 10a' is decreased so as to thereby increase the velocity of the fluids passing'through the latter portion of the coil, thus tending to prevent overheating of the fluid. Fresh charging stockiis'in# troduced ythrough the line 14 to the lower row oi the inner coil 40 and a transfer lineV 43'directs the oil from'the coil 40 to the still 11,. abaiile 44 being provided for directing the flow of the oil in the still ll. Thus'the condensate oil isintroduced into `the coil 10a at a relatively coolerportion of the furnace 26 and in transit through' the coil 10a is subjected to the action of combustionV gase of progressively increasing ltemperatures:to thus rapidly raise the oil to the cracking temperature desired and then when the oil thus highly heated enters that section of the coil which is provided with the heat exchange coil 40 the rapid increase in heat may be arrested although the condensate oil may be held at approximately the temperature to which it has been heated or at any cracking temperature desired during the rest of its passage through the coil. The relatively cool fresh charge which is introduced through the line 14 to the lower row of the coil 40 may be raised to a cracking temperature by reason or the heat obtained from the heated products in the outer coil 10a.

The coil 40 is shown disposed interiorly of the coil 10a but in a modification of the invention the coil 40 may be arranged exteriorly of the coil Although the temperature and pressure conditions employed in the practice of the invention will necessarily vary within comparatively wide limits it may be stated that ordinarily temperatures in excess of 900 F. are employed in the coil 19a and that preferably the temperatures used are of the order of 1G00" F. to 1200 F. under a substantial superatmospheric pressure, depending more or less upon the boiling point of the charging stock employed. Thus the condensate oil in transit through the coil 10a may be rapidly brought to a temperature approximating 1000 F, to 1200" F. and then upon entering that portion of the coil 10a which is in heat exchange with the coil 40 any further increase in temperature may be stopped although the cil may still be held at a cracking temperature during the rest of its passage through the coil 10a. 1n other words, after the oil has been heated in transit in the coil 10a to the maximum temperature desired for cracking it is, by reason of the heat exchange with the relatively cooler oil passing through the coil 40, subjected to a soaking action, without necessarily any further increase in temperature, so that cracking may be continued without, however, causing the excessive production of xed gases or coke. The fresh charging stock introduced through the line le upon being passed through the heat exchange coil 40 may be brought to a distilling temperature sufficient for the distillation of desired fractions or preferably is brought to a cracking temperature relatively low as compared with 'the maximum temperature reached in the coil 10a. Thus the charging stock may be heated to for example approximately '750 F. to 850 F. in the coil 40.

When the coil 10 is employed the condensate oil in transit therethrough is rapidly raised to a cracking temperature ordinarily in excess of 900 F. and preferably of about 1000 F. to 1200* F.

and then upon being commingled with the rela-v tively cool fresh chargingV stock introduced through the lines 15 the temperature of the stream of oil passing through the coil 10 is lowered, although preferably not below a cracking temperature so that both constituents in the fresh charge as well as constituents in the condensate oil may be subjected to cracking during their transit through the latter section of the coil 10.

When using the indirect method of heat exchange the preferred method of operation is to pass the relatively cool fresh charging stock through the inner coil 40 in counter current flow to the more highly heated condensate oil passing through the coil 10a so as to thus raise the temperature of the fresh charging stock, by reason of the heat exchange with the condensate oil, and to discharge the fresh charging stock into the still 11 when the oil has attained approximately the temperature of the condensate oil flowing in counter current with it. In other words, the fresh charge as it enters the bottom row of tubes of the coil 40 will be at a relatively low temperature, as compared to that obtaining in the bottom row of the tubes of the coil 10a, but as the fresh charging stock flows through the successive rows of tubes of the coil ll0 the temperature of the oil is progressively heated until it may approximate the temperature of the adjacent oil in counter current iiow in the coil 10a. The fresh charging stock may, if desired, be discharged from the coil l0 before it has been brought to a temperature equal to that obtaining in the coil 10a but it is generally preferable to terminate the coil i0 and pass the oil to the still 11 at approximately that point where the temperature curves of the two flowing streams of oil cross.

In carrying on the process it is preferable to do the bulk of the cracking, or preferably substantially all of it, in the coil 10, or in the coils 10a and 4:0, and retain the still 11 for distillation mainly. Although some cracking may be carried on in the still 11 it is preferable, as stated, to rely on the coils 10 or 10a and 40 to do the cracking so as to facilitate the distilling action carried on in the still. l1 for the purpose civ obtaining the maximum quantities of cycle stock for charging to the coil 10 or lcd as well as to obtain the maximum quantities of gasoline or light distillate. If desired, a material pressure differential may be maintained between the coil 10 and the vstill 11 as by means of a pressure regulating valve 45 and a pressure differential between the coil 10a and coil au and the still l1 may be had by means of the valves 46 and 47, respectively, in the lines 41 and 43, respectively. If desired, however, the operation may be carried on without any pressure diierential other than that which may occur by reason of the irictional resistance in the coil. The operation may be carried on at relatively high superatmospheric pressures or at relatively low pressures, may be desired.

The invention contemplates ak preferred method of operation in which the cycle stock or condensate oil that is introduced to the coil 10 or 10a is considerably in excess in quantity of the fresh charge which is introduced through the lines 15 into the coil 10 or through the line 14 into the coil di) and thus the more highly heated .oil will exceed in volume vthe less highly heated fresh charging stock with which it is brought into heat exchange and the more highly heated oil may be pumped at a higher rate than the less highly heated oil.

Steam may be introduced into the still 11 to aid in the distillation therein. Steam may be passed into the vapor space of the still 11 in order to overcome the effect of any foaming that may take place in the still and to thus prevent the carrying over of any tarry or residual constituents into the dephlegmator 12.

Although the preferred embodiment of the invention has been set forth in connection with apparatus having particular construction and arrangement of parts and mode of operation, it is obvious that 'various changes and modifications may be made therein, while securing to a greater or less extent some or all of the benets of the invention, without departing from the spirit and scope thereof. Therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. The process of converting higher boiling hydrocarbon oils into lower boiling ones that comprises passing a condensate oil derived from the process through a section of a heating coil exposed to furnace gases tc rapidly raise the oil to a relatively high cracking temperature, passing the oil thence into another section of the heating coil which is also exposed to the furnace gases but which is disposed in heat exchange with another coil through which a relatively cooler oil is passed to thereby prevent the temperature of the condensate oil undergoing cracking from rising materially and to maintain it at substantially the cracking temperature to which it had been heated, passing the highly heated oil undergoing cracking from the heating coil into a chamber and subjecting it to vaporization therein, passing fresh charging stock as the relatively cooler oil through said other heat exchange coil to thereby raise said charging stock to a cracking temperature lower than the maximum obtaining in the higher temperature heating coil, passing the oil thus heated into said vaporising chamber, dephlegmating vapors evolved in the vapcrizing chamber to form a vapor fraction and a liquid fraction, introducing liquid thus obtained as charging stock to the higher temperature coil and condensing the vapor fraction.

2. The process of converting higher boiling Vhydrocarbon oils into lower boiling ones that comprises passing a condensate oil derived from the process through a section of heating coil exposed to furnace gases toV rapidly raise the oil to arelatively high cracking temperatiue, passing the oil thence into another section of the heating coil which is exposed to the hotter furnace gases but which is disposed in heat exchange with another coil through. which a relatively cooler oil is passed to thereby prevent the temperature of the condensate oil undergoing cracking from rising materially and to maintain it at substantially the cracking temperature to which it had been broughhpassing the highly heated oil undergoing cracking into a chamber and subjecting it to vaporization therein, passing fresh charging stock as the relatively cooler oil through said other heat exchange coil to thereby raise it to a temperature lower than that obtaining in the higher temperature coil but suficient for vaporization, passing the oil thus heated into said vaporizing chamber, dephlegmating vapors evolved in the vaporizing chamber to form a vapor'fraction and a liquid fraction, introducing liquid thus obtained as charging stock to the higher temperature coil and condensing the vapor fraction.

3. Apparatus for converting higher boiling hydrocarbon oils into lower boiling ones that comprises a vaporizing chamber, a dephlegmator in vapor communication therewith, heating means formed to provide a heating zone of progressively increasing temperature, a heating coil arranged to be heated thereby to a cracking temperature and having an inlet in the cooler portion of the heating zone so that oil in transit through the coil may be subjected to progressively increasing temperatures, means for removing reflux condensate from the dephlegmator and introducing it to the inlet of the heating coil for passage therethrough, a conduit disposed in heat exchange relation with a portion of said heating coil located in the higher temperature part of the heating zone, means for introducing fresh charging stock into said conduit for passage therethrough and means for conducting oil from said heating coil and conduit to the vaporizing chamber.

Li. The process of treating hydrocarbon oil which comprises passing the oil through a coil which is subjected to increasing temperatures from the inletl to the outlet thereof, these temperatures being sufiicient to raise oil reaching an intermediate point of said coil tol a cracking temperature and the temperature between said intermediate point and said outlet being so high as without added cooling to raise said oil to a teA perature at which the production of undesirable fixed gases and carbony is brought about; and cooling the portion of said coil between said intermediate point and said outlet by indirect heat exchange with fresh relatively cool charging stock of such quantities that said oil first mentioned is maintained during the rest of its passage through said coil at substantially the temperature vwhich it attained at said intermediate point and said fresh charge is raised during its heat exchange relationship with coil to a cracking temperature, increasing the velocity of said oil during its passage in heat exchange relationship with said fresh charging stock, 'injecting both said oil and said fresh charging Ystockinto a still wherein vaporization is accomplished, removing the resulting vapors, condensing heavier fractions thereof to form a condensate, and returning said condensate to the inlet of said coil to constitute the oil first mentioned.,

HORACE A. FOUTS,

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