US1961692A - Apparatus for cracking heavy hydrocarbons to produce lighter hydrocarbons - Google Patents

Description

E. W. ISOM June 5, 1934.

APPARATUS FOR CRACKING HEAVY HYDROCARBONS TO PRODUCE LIGHTER HYDROCARBONS Original Filed Aug. 28, 1922 INVENTOR BY XT FORNEYS Patented June 5, 1934 UNITED STATES APPARATUS FOR CRACKING HEAVY HY- DROCARBONS TO HYDRO CARBON S PRODUCE LIGHTER Edward W. Isom, Scarsdale, N. Y., assignor to Sinclair Refining Company, Chicago, 111., a corporation of Maine Original application August 28, 1922, Serial No.

584,711. Divided and this application June 10, 1927, Serial No. 197,781

3 Claims.

In the process commonly employed for converting higher into lower hydrocarbons, more particularly for converting gas oil and the like into gasoline, a body of the heavy hydrocarbon is distilled under such pressure that its temperature is raised in the liquid phase to a point at which the hydrocarbons composing the oil, or part of them, are decomposed to lower or lighter hydrocarbons. Another known process for converting higher into lower hydrocarbons is to crack the hydrocarbons in the vapor phase by first converting them into vapors and then subjecting them while in that state to the cracking temperaure.

The present invention relates to a new and improved apparatus for cracking heavier oils, for the manufacture of gasoline, etc., in which a part of the oil is cracked in the vapor phase and a part in the liquid phase, and in which the vapor phase and liquid phase cracking operations are combined in a particularly advantageous manner. The preferred method of operation of the apparatus of the present invention involves cracking a part of the oil in the vapor phase and introducing the resulting products of the vapor phase cracking operation directly into a pressure still containing a body of oil maintained at a cracking temperature and pressure. By introducing the products of the vapor phase cracking operation into the-liquid phase cracking still in this way, the products of the vapor phase cracking operation are caused to comzningle and combine with the liquid and gaseous or vaporous products in the liquid phase still, and the products of the vapor phase cracking are thus subjected to the cracking conditions prevailing in the liquid phase still. The heavier or less volatile products of the vapor phase cracking operation become admixed with the charge in the liquid phase still, while the gases and lighter vapors from the vapor phase cracking operation commingle with the gaseous and vaporized products in the liquid phase still and, to a greater or less extent, appear to react or'combine with such products.

This application is a division of my application filed August 28, 1922, Serial No. 534,711.

According to one desirable method of operating the apparatus of the invention the vapor phase cracking operation is carried out at a much higher temperature than that required for the liquid phase cracking operation, and the superheated products from the vapor phase cracking operation are introduced into the body of oil in the liquid phase pressure still, thereby heating it internally. For example, the vapor phase crackheating this body of oil and being themselves cooled to the temperature prevailing in the liquid phase pressure still which may be, for example, a temperature of 700 to 750 F. By combining a high temperature vapor phase cracking operation in this way with the operation of a liquid phase pressure still, the charge in the pressure still can be heated internally to the cracking temperature, the charge of the pressure still being cracked at a considerably lower temperature than that used in the vapor phase cracking operation. The entire heating of the liquid phase still can be supplied internally by the highly superheated vaporous product from the vapor phase cracking operation, thus avoiding the application of external heat to the still walls and preventing the formation of carbon deposits thereon and making possible the treatment of heavy oils and residues, and the reduction of these heavy oils and residues to a heavy sludge or even to coke. Instead of introducing the vapors from the vapor phase crackingoperation into the body of liquid in the liquid phase still, they may be introduced into the vapors in the vapor space of the still, thus heating the vapors in the still and being themselves cooled. Interaction between the admixed vaporous products is thus promoted. Or a part of the products from the vapor phase cracking operation can be introduced into the liquid body in the pressure still and a part into the vapor space above the body of liquid.

The vapor phase cracking operation can be carried out in diiierent cracking apparatus and under different conditions. In the operation of the combined apparatus of the present invention, however, it is particularly advantageous to utilize, in the vapor phase cracking operation, the kerosene and lighter gas oil fractions which are not readily cracked, except at high pressures, in a liquid state. Such oils can be readily vaporized and can be subjected to the necessary cracking temperature without excessive c'arbon formation. 7 The'cracking operation can readily be carried out, for example, in externally heated coils throughwhich the oil vapors are passed ata high velocity and brought to the cracking temperature, e. g. around 1000 F. The vapors, forex,-

ample, of kerosene or light gas oil, can be sub- -jected to cracking without admixture of other gases or vapors, or the oil vapors may be admixed with a greater or less amount of steam or of the permanent gas resulting from the combined cracking operations, or with other suitable gases. The pressure maintained in the vapor phase cracking apparatus can be varied but, in general, it should be as high or higher than that maintained in the pressure still so that the pressure will be sufficient to force the cracked products into the pressure still. Where a long pipe coil or series of coils is used in the vapor phase cracking operation, a considerably higher pressure may be necessary at the feed end of the coil to overcome the frictional resistance of the oil and oil vapors through the coils. Where the pressure maintained in the pressure still is around 60 to 100 lbs. asufiiciently higher pressure should be maintained in the vapor phase cracking system to insure the discharge of the products thereof into the liquid phase pressure still.

The temperature as well as the pressure, in the vapor phase cracking system, can be varied. For example, by using a higher. temperature, an increased amount of aromatic hydrocarbons, such as benzol and toluol, can be produced by the vapor phase cracking operation. A temperature of around 1100 F. anda pressure in excess of 60 lbs. can thus be used, for example, where an increased amount of aromatic hydrocarbons is desired in the final motor fuel or gasoline produced by the combined cracking operations.

The liquid phase cracking operation carried out in the pressure still is likewise capable of considerable variation; and different constructions of pressure stills can be used. Where the products fromthe vapor phase cracking operation are introduced into the body of oil in the pressure still, they will cause agitation of this oil, and, where they are at a much higher temperature they will heat the body of oil internally, and the heavier products from the vapor phase cracking operation will become admixed with the charge in the still while the gases and lighter vapors ,will admix with the vapors formed in the pressure still and the resulting lighter vapors, after such further reaction as may take place, will escape from the pressure still as a composite distillate. The introduction of the vapor phase products into the liquid phase pressure still, and the heating of the oil internally by such products, enables the cracking operation to be carried out at a lower temperature and pressure than when the oil is heated externally.

The temperature and pressure in the pressure still can be varied. A pressure of around to lbs. and a corresponding. temperature, can thus be employed, or the operation can be carried out at a lower temperature and pressure, for example, from 60 to 90 lbs. as well as at higher pressures of lbs. or more. The charge in the pressure still will have added to it the heavier products from the vapor phase cracking operation, and these heavier products will then be subjected to further cracking.

The advantages of the invention will be further described and illustrated in connection with the accompanying drawing which illustates, in a somewhat conventional and diagrammatic manner, one form of apparatus embodying the invention. It is to be understood, however, that the specific disclosure is for the purpose of illustration and exemplification and that the scope of the invention is not limited thereto but is defined in the following claims in which I have endeavored to distinguish it from the prior art so far as known to me, without, however, relinquishing or abandoning any portion or feature thereof.

The liquid phase still 55 shown in the drawing is the ordinary shell form of still. A furnace 56 is provided for assisting in heating the oil to start the process or to overcome the radiation losses or as an auxiliary to the main heating of the oil internally. During the main operation of the process this furnace 56 may not be used or may be used only to a suflicient extent to prevent undue radiation losses, the internal heating of the coil being relied upon for carrying out the cracking operation.

The vapors resulting from the combined cracking operation escape through the pipe 57 which may be provided with a pressure reducing valve (not shown) and then pass to the exchanger 12 where a portion of the vapors is condensed. When this exchanger acts as a reflux tower the condensate returns to the still through the pipes '70 and 58 and enters the body of oil through the perforated pipe 59. Instead of refluxing the condensate to the still it may be drawn ofi through the branch connection 69 to the reservoir 19 for admixture with the condensate from the exchanger is flowing to the reservoir through pipe 18 or it may be drawn off to a separate reservoir (not shown). The vapors from the exchanger 12 escape by pipe 15 to a second exchanger 16 where a further portion of the vapors is condensed. When liquid condensate is body, by the vapors discharged from the vapor phase cracking apparatus through the pipes 60 and 63, the pipe 63 being a perforated pipe for distributing the vapors and bringing them into intimate contact with the oil. A check valve 61 and hand-valve 62 for controlling or assisting in controlling the flow of cracked vapors are provided in the pipe 60. A tar draw-off from the still 55 is indicated at 6'7 and may be used when the process is carried out as a continuous process. This tar draw off is not used when the charge is run down to coke.

The illustration of apparatus for carrying out the vapor-phase cracking operation is more or less conventional and diagrammatic, but in practice it will be understood that a sufiicient number or length of pipes will be used in the coil or coils 23 to insure vaporizing the oil and subjecting it to the necessary. temperature for effecting the vapor phase cracking to a greater or less extent of the oil. When valve 62 is open, the products from the vapor phase cracking operation, if

under a pressure somewhat in excess of that in the pressure still, will be forced into the pressure still. The pressure in the vapor phase cracking coil, in such a case, would be controlled by the pressure on the liquid phase still and the rate of feed to the vapor phase cracking coil. The specific form and construction of the furnace employed, as well as the size and number of the pipes employed, in the vapor phase cracking apparatus can be varied, but in the form shown the furnace is heated by a burner 29 and the products of combustion pass ina zig-zag course and leave the furnace through a stack flue 30 at the bottom.

In order to assist inmaintaining a uniform furnace temperature, arrangement is made for recirculating a greater or less amount of the gases from near the exit of the furnace and reintroducing them so that they become admixed with the fresh products of combustion from the firebox 24. A return flue 31 is shown in the drawing leading from near the exit to a point near the inlet and provided with an injector for =forcing the recirculation of the products of combustion to a greater or less extent. The hot products of combustion are thus diluted with the recirculated cooler products of combustion. By regulatingthe amount of gases recirculated and the heat supplied to the furnace by the burner, it is possible to obtain a uniform and definite temperature, for example, a temperature of around 1000 F. at the exit of the cracking coils.

The vapor phase cracking apparatus may be supplied with the intermediate or kerosene condensate from the reservoir 19 by means of pipe 20 or with charging stock of a similar character from the supply tank 44. The fresh stock for the liquid phase cracking operation, e. g., gas oil, can be supplied from the reservoir or supply tank 34 and employed to assist in condensing the vapors in exchangers l2 and 16 being thereby preheated. This preheated oil can then be supplied through the pipe 64 tothe pipes 58 and 59, and thus introduced into the body of oil in the still. A check-valve 65 and hand-valve 66 are provided in the pipe at the connection between the pipe 64 and the pipe 58. Meters are shown at 37 and 46. The fresh oil thus fed to the still is mingled with any reflux and the two are introduced into the oil together. The vapor phase cracking apparatus is supplied with oil by means of the pump 21 and pipe 22 at a pressure sufficient to force the resulting products, after having been subjected to the vapor phase cracking operation, into the main body of oil in the still 55. These products from the vapor phase cracking apparatus pass through the tar separator 26 and thence through the pipes 60 and 63 into the still in the manner above described.

The lightest portion of the vapors, which is uncondensed in the exchangers 12 and 16 and which contains the desired cracked distillate or pressure distillate, escapes by pipe 17 to any desired form of final condenser. As these condensers are common and well known it is not considerednecessary to illustrate them. A pressure reducing valve may be provided in the pipe 57 to permit the exchangers 12 and 16 to be operated at approximately atmospheric pressure, while, by opening this valve and regulating the pressure by the valve in the pipe 17 the exchangers 12 and 16 can be kept at the same pressure as that maintained in the still, while the final condenser can be kept at substantially atmospheric pressure; or by regulating the pressure at the outlet of the final condenser, the final condensation can be carried out under pressure.

- In the operation of the combined apparatus illustrated, the still 55 is charged with the oil, such as gas oil, which is to be subjected to the liquid phase cracking operation. This oil may be heated before it enters the still or it may be heated in the still to a temperature approximating that at which cracking takes place. The furnace 56 may be used in this preheating operation. The kerosene or other oil in the reservoir 19 or in the supply tank 44 is then forced through the .to a greater or less extent.

vapor phase cracking coil where it is subjected to a cracking temperature and where cracking takes place to a greater or less extent. The resulting cracked vapors may thus be heated to a temperature around 1000 F. under a pressure in excess of that maintained in the pressure still 55 and then discharged into the body of oil. The highly superheated vapors are thus cooled to approxi- -mately the temperature of the oil while the oil is in turn heated. The heavier products from the vapor phase cracking operation are added to the body 05 liquid oil while the lighter vapors and gases commingle with the vapors and gases from the liquid phase cracking operation. The liquid phase cracking operation is thus carried out with effective internal heating of the body of oil and with the production of a resulting distillate of a composite character containing the lighter products from the vapor phase cracking operation as well as the lighter products from the liquid phase cracking operation, together with such further amounts of light vapors as may result from the reaction of the admixed gases and vapors.

The lighter products produced by the cracking of oil in the vapor phase contain a considerable amount of unsaturated compounds and have a relatively high iodine value. The composite product of the combined liquid phase and vapor phase cracking operation has a much lower iodine value than the vapor phase product and is comparable with that obtained in liquid phase cracking operations carried out under pressure. The amount of permanent gas formed in the vapor phase cracking of oil is generally much higher than that with liquid phase cracking under pressure, but the amount of gas formed by the combined process is comparable with that obtained by straight pressure distillation. It is; probable therefore that a considerable amount of reaction takes place between the products of the vapor phase cracking operation and those of the liquid phase cracking operation whereby the permanent gases and lighter vapors react with each other The cooling of the highly superheated vapors from the vapor phase cracking operation, by introducing them into the body of liquid, prevents further objectionable overcracking. For example, the superheated vapors which are heated in the vapor phase cracking coils to around 1000 F. will be cooled to a considerably lower temperature, e. g., around WOO-750 F. when they are brought into intimate contact with the body of liquid oil. By carrying out the vapor phase cracking process in this way bringing the vapors up to the superheated stage necessary for cracking, and then almost immediately stopping the reaction by introducing them into a mass of cooler oil, the further over"-' cracking with resulting formation of an increased amount of unsaturated compounds is prevented. The portion of the vapor phase products which is condensed when subjected to this cooling effect is then further subjected to the liquid phase cracking conditions, and such portions as can be further cracked in this way are subjected to the cracking operation along with the liquid charged into the pressure still; while such fractions as are not readily treated in the pressure still and as are not desired in the final distillate can be returned to the vapor phase cracking process.

The respective portions of the cracked products which can best be treated in the vapor phase and in the liquid phase cracking operations can thus be treated in these respective operations,

the lighter fractions too heavy for the final dil- 5 tillate, being recycled repeatedly through the vapor phase cracking coil where the vapors are heated to high temperatures for comparatively short periods, and the lighter fractions are thus progressively cracked into products which finally leave the combined operations as the desired distillate or as permanent gas or residue. This recycling of the lighter fractions (for example, those corresponding generally to kerosene or light gas oil and which are not readily cracked in a pressure still except at high pressures) makes it possible to subject them repeatedly to a cracking temperature in the vapor phase, with partial cracking of the vapors,. and with avoidance of prolonged exposure and overcracking at elevated temperatures, the vapors being heated to the cracking temperature for comparatively short periods and being then cooled by introduction into the body of liquid oil at a lower temperature. The separation orthe lighter or intermediate fractions so that they are not returned to the pressure still also makes for more efficient operation of this still, since the heavier oils can be more readily cracked, and at a lower pressure; while the lighter fractions are those most advantageously treated in the vapor phase.

Where it is desired to subject a portion of the heavier condensate from the pressure. still to cracking in the vapor phase this can be accomplished by closing the valve in the pipe '70 so as to prevent refluxing of the heavier oil to the still and opening the valve in the pipe 69 so that the heavier condensate from the exchanger 12 will pass to the reservoir 19. In this way the heavier and lighter fractions can be combined for treatment in the vapor phase.

In referring to the heavier and lighter fractions of the condensed vapors it will of course be understood that the final condensate will be the desired cracked distillate or pressure distillate and will contain the gasoline; the lighter and heavier condensates referred to being the fractions which are separated from the vapors before they are subjected to the final condensation.

In the operation of the apparatus illustrated,

the running of the charge to dryness can be carried out with shutting ofi" of the feed by closing the valve 66 in the pipe 58 and opening the valve in the pipe 68 which will lead the preheated oil to another still or to a place of storage. The refluxing of the heavier condensed vapors back to the still through the pipes 58 and 59 can also be discontinued by closing the valve in the pipe 70 and the condensed vapors can then be led to the receptacle 19 by opening the valve in the pipe 69. When the still is operated in this way the cracking operation will continue without the introduction of further amounts of oil until the cracking of the residue constituents has been carried to completion or to the desired point. Inasmuch as the walls of the still are not heated externally to high temperatures, the coke or coke-like residue remaining in the still at the end of the operation will be relatively easy to remove.

I claim:

1. An apparatus for treating hydrocarbon oil, comprising a heating coil disposed within a furnace, an enlarged reaction chamber, means connecting said coil with such chamber, a dephlegmator, means for conveying vapors from said enlarged chamber to said dephlegmator, means for introducing oil to said dephlegmator to act as a dephlegmating medium for the vapors therein, a conduit for conveying reflux condensate from said dephlegmator to said enlarged reaction chamber, a valve in said conduit, a second conduit for conveying the reflux condensate directly to the heating coil when said valve is closed, and means for maintaining a self-generated superatmospheric pressure on the oil undergoing conversion in the apparatus.

2. An apparatus for treating hydrocarbon oil, comprising a single-pass heating coil disposed within a furnace, an enlarged reaction chamber, means connecting said coil with such chamber,

a dephlegmator, means for conveying vapors from said enlarged chamber to said dephlegmator, means for passing relatively cool oil in indirect heat exchanging relation with the vapors in said dephlegmator to act as a cooling and dephlegmating medium for the vapors therein, a conduit for conveying reflux condensate from said dephlegmator to said enlarged reaction chamher, a valve in said conduit, a second conduit for conveying the reflux condensate directly to the heating coil when said valve is closed and means for maintaining a self-generated superatmospheric pressure on the oil undergoing conversion in the apparatus;

3. An apparatus for converting high boiling hydrocarbon oils into lower boiling products in combined vapor-liquid phase, in combination, a single pass heating coil adapted for cracking oil under pressure and high temperature in the vapor phase, an unheated still, means for supplying oil under pressure thereto, means for delivering the highly heated evolved vapors from the vapor phase converting means into the body of oil in said still to raise and maintain the oil at a temperature sumcient for liquid phase conversion, means for removing from the still the vapors evolved by the combined vapor liquid phase operation and for conveying the vapor mixture to a dephlegmator, means for passing relatively cool oil in heat exchanging relation with the vapors in said dephlegmator to act as a cooling and dephlegmating medium for the Vapors therein, and means for conveying condensate from said dephlegmator for retreatment to both the vapor phase cracking means and to the still, including means for controlling the relative proportions of said condensate to be re-' 1 rid

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